Ingredients
Method
Step 1: Build the base
- In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth and glossy.
Step 2: Whip for structure
- Add the eggs and vanilla extract. Whip until the mixture turns pale and off-white and slightly thickened—this step helps create that classic thin, crackly brownie top.
Step 3: Incorporate the oil
- Whisk in the vegetable oil until fully combined.
Step 4: Add dry ingredients
- Add the cocoa powder, all-purpose flour, cornstarch, and baking soda. Fold just until mostly smooth, being careful not to overmix.
Step 5: Bake
- Pour the batter into a greased and parchment-lined square pan, smoothing the top.
- Bake at 350°F for 21–23 minutes, until the edges are set and the center is just soft.
Step 6: Cool
- Let the brownies cool completely while preparing the frosting.
Step 7: Make the hot cocoa frosting
- In a stand mixer, whip the butter on high speed for 3–4 minutes, until light and fluffy.
- Add the powdered sugar and hot cocoa mix and beat until thick and smooth. Add the heavy cream and whip on high for about 2 minutes, then mix in the vanilla.
- Spread the frosting evenly over the cooled brownies and sprinkle mini marshmallows on top.
Step 8: Set & serve
- Let the brownies chill for 20–30 minutes before slicing.
- Enjoy fresh, or store in the refrigerator for up to 10 days.