Preheat oven to 350ºF (176ºC) and prepare an 8x8" (20x20cm) baking pan by lining it with a sheet of parchment paper or aluminum foil, leaving a few inches of overhang on the sides to allow for easy removal. Grease if using foil and set aside.
Add coconut oil and chocolate chips to a small saucepan set over low heat. Stir until oil and chocolate have melted before removing from heat and setting aside to cool slightly.
Using a handheld mixer or a stand mixer,**** beat together eggs, sugar, and vanilla extract until smooth, about 2 minutes. Add melted chocolate mixture and mix until well combined. Reduce speed to low and add cocoa powder, arrowroot powder, and salt; mixing until fully combined and scraping down the sides of the bowl as necessary. Batter should be thick and smooth.
Pour batter into prepared pan, spreading it evenly with a spatula. Bake for 25-30 minutes, until center is set. Remove from oven and let cool in pan for about 15 minutes before removing and transferring to a wire rack to cool completely. Cut into squares and serve.
Notes
* Can sub with melted butter, but you might not get the crackly tops.** Can sub with granulated sugar.*** Can sub with cornstarch.****You don't have to use a mixer, but I find it easier. If not using a mixer, be sure to whisk eggs for about 1 minute and until they are bubbly.