Peanut butter lovers, these Chewy Peanut Butter Oatmeal Monster Cookies are for you! I’m confident you’ll fall in love with these soft, thick, scrumptious sweet treats and this will become your go-to cookie recipe!

cookies with REESE'S Pieces and chocolate chips

The classic Monster Cookies are made with peanut butter, oats, chocolate chips, and M&Ms. And if you google Monster Cookies you’ll find many similar recipes. I really wanted mine to be the BEST and after several tries, I’m sharing the most perfect Monster Cookies with you today. I do want to warn you, though, these Monster Cookies are VERY dangerous. Dangerous to have around because you’ll want to gobble up far too many of them! Consider this your warning. 😉

mixing Monster Cookie ingredients in a glass mixing bowl

What Makes These Monster Cookies the BEST?!

I may have mentioned this before, but I take my cookie game pretty seriously. Like, we’re talking Level: Cookie Snob. There are not enough meals in this lifetime to waste even one bite on a medium-good cookie. No, friends. We go big (and soft, and chewy, and filled with texture) or we go home.

My easy monster cookie recipe yields extra soft and thick cookies and you don’t need to chill the cookie dough! These cookies are seriously so easy to make with basic ingredients. You probably have just about everything needed to whip up these bad boys, in your pantry right now.

And by the way, when I say “monster” cookies… I mean MONSTER cookies. No teeny, tiny, pathetic cookies here, folks. I’m a firm believer that a good cookie should be the size of your head (give or take a little 😉 ), not the size of a grape. This recipe calls for 1/4 cup of dough per cookie, and although it may sound a little excessive, trust me on this one. The cookies will bake up perfectly chewy on the outside, but still soft and tender on the inside. This recipe will yield 12 massive monster cookies. I obviously love these BIG, but if you prefer a smaller cookie, use about 2 tablespoons of dough per cookie and you’ll have about 24 cookies total.

monster cookies stacked one on top of another

Tips & Tricks and How to Make the Best Monster Cookies

This recipe starts with beating the brown sugar, butter and peanut butter together for at least 3 minutes. It may seem like a really long time and totally unnecessary, but it’s an important step. It gets the sugar incorporated into the butter and it’s nice and fluffy. You know it’s ready when the mixture becomes very light in color. You’ll then lightly mix in the egg and vanilla.

While the sugar and butters are mixing, you can be combing the dry ingredients (flour, baking soda, cornstarch, baking soda, salt and oats) in a separate bowl. When measuring flour, use the “spoon & level” method. Do not scoop the flour out of the container/bag with your measuring cup. Scoop the flour and you could end up with 150% of the correct measurement. Rather, using a spoon, scoop the flour into the measuring cup. Do not pack the flour down and do not tap the measuring cup– both cause the flour to settle in the cup. After you’ve spooned the flour into the measuring cup, use the back of a knife to level off the top of the measuring cup. You can also use a food scale to measure the flour and other ingredients in grams. This is what I do because I want the recipe to be absolutely perfect for you guys.

Thanks to a secret ingredient, cornstarch, these cookies are perfectly thick & chewy, with a slightly crunchy edge and a super soft baked center. If you’ve never added cornstarch to cookies then you have been missing out. It’s only a small amount, but it makes a HUGE difference in the texture of the cookie. Soft-baked inside with a slightly chewy outside. Perfection ♥

monster cookie dough on a baking sheet

Use quick oats. Why? Quick oats are more finely cut whole oats and will give the Monster Cookies a more uniform texture. Furthermore, quick oats will act more as a binder since the consistency is more powdery. If you don’t have quick oats, pulse your whole oats in the food processor a few times to break them down.

Now gradually add the combined dry ingredients to the wet ingredients and only mix until just combined. Finally, stir in the mini chocolate chips and REESE’S Pieces by hand. Measure out 1/4 cup cookie dough for each cookie, roll and place on the prepared baking sheet.

These cookies spread very little while baking and will still be puffy when they come out of the oven. Feel free to take the bottom of a drinking glass and gently press down on the tops of the cookie to flatten them slightly and make them look more like a cookie. I like to keep them puffy, but just press a few additional REESE’S Pieces on the tops of the cooked cookies. This will naturally “un-puff” the cookies and they will flatten out slightly.

You definitely do not want to overbake these cookies. REMEMBER that they will firm up and cook a bit more while they are cooling on the cookie sheet. I recommend waiting the full 5 minutes before transferring them to a wire cooling rack. And if you have the patience for it, I recommend waiting until the cookies are fully cooled before enjoying. They are delicious warm, but will be crumbly until they have cooled.

monster cookies on wire cooling rack

Try my family’s other favorite dessert recipes!

The BEST Banana Pudding Recipe

Easy Cream Cheese Pie {video}

Easy Lemon Pound Cake

Easy Strawberry Lemonade Poke Cake {video}

Please let me know how your cookies turn out in the comments! They’re a real treat and I hope they become your new favorite cookie recipe. I’d also LOVE to see a photo of the finished product – tag @kimscravings on Instagram. Be sure to subscribe to our mailing list to receive more healthy delicious recipes straight to your inbox.

Monster Cookies stacked on a white plate

cookies with REESE'S Pieces and chocolate chips
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Chewy Peanut Butter Oatmeal Monster Cookies

Big, chewy peanut butter oatmeal cookies loaded with sweet chocolate chips and yummy REESE’S Pieces candies!
Author: Kim


  • 1/2 cup butter,, softened
  • 1 cup brown sugar
  • 1/2 cup creamy peanut butter
  • 1 large egg
  • 2 teaspoons vanilla extract
  • 3/4 cup all-purpose flour
  • 1 teaspoon baking soda
  • 1 teaspoon cornstarch
  • 1/4 teaspoon baking powder
  • 1/4 teaspoon salt
  • 1 1/2 cups quick oats
  • 1/2 cup mini semi-sweet chocolate chips
  • 1 cup REESE’S Pieces or M&M candies


  • Preheat oven to 350ºF and line baking sheets with parchment paper and set aside.
  • In a large bowl, cream together butter, brown sugar, and peanut butter with a hand or stand mixer until light and fluffy, about 3-4 minutes. Mix in the egg and vanilla, scraping down the sides of the bowl as needed.
  • In a separate bowl, add the flour, baking soda, cornstarch, baking powder, salt, and quick oats; whisk to combine. With the mixer on low speed, slowly add the flour mixture to the wet ingredients and mix until just combined. Stir in the chocolate chips and REESE’S Pieces candies by hand.
  • Measure out ¼ cup balls of dough and place them on the baking sheets. Bake the cookies for 11-13 minutes, until the edges are just starting to brown and the top still looks slightly undercooked. Remove from the oven and cool for 5 minutes on the baking sheet before moving them to a wire rack to cool completely. Before these have cooled completely, they will be crumbly. I suggest letting them cool completely before tasting.
  • Store cookies covered at room temperature for up to 1 week.


As written, this recipe makes 12 very large cookies. You can certainly make 24, more normal-sized cookies.  
3-4 minutes will seem like a long time to mix the sugars, peanut butter, and butter but it's really important. The dough will become much lighter in color and look fluffy. That's when you know you have blended it long enough.
For a flatter cookie, take the bottom of a drinking glass and gently press down on the cookie right after they come out of the oven OR just press some additional candies on the tops of the cooked cookies and that will naturally press them down into more of a cookie shape, I always do this and it works so well. The cookies don't spread much at all while baking.
Natural peanut butter does not work well in this recipe. I used the original Jif.
Press some additional candy pieces and chocolate chips on top of the cookie dough balls, before putting cookie sheet in the oven, for a pretty presentation.
Freezing Instructions: Baked and cooled cookies freeze well for up to 3 months. Unbaked cookie dough balls freeze well for up to 3 months too. Bake frozen cookie dough balls for an extra minute, no need to thaw.
Serving: 1cookie, Calories: 324kcal, Carbohydrates: 39.5g, Protein: 5.7g, Fat: 17.3g, Saturated Fat: 7.8g, Polyunsaturated Fat: 1.6g, Monounsaturated Fat: 2.7g, Cholesterol: 35.4mg, Sodium: 218.7mg, Potassium: 69.3mg, Fiber: 2.7g, Sugar: 23.2g, Vitamin A: 345IU, Vitamin C: 0.9mg, Calcium: 20mg, Iron: 2.2mg

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