Preheat the oven to 350℉/176℃. Line the muffin tin with muffin liners and set aside.
In a medium-sized bowl, add in the dry ingredients. Stir to combine and set aside.
1 1/3 cups all-purpose flour, 1/4 cups cocoa powder, 1/2 tsp baking soda, 1/2 tsp baking powder, 1/4 tsp salt
In a microwave or using a double boiler method, melt the butter. Then add in the chocolate chips and mix together until the chocolate has melted and the mixture is completely smooth and combined together. Then transfer into a large bowl.
1 1/4 cups semi-sweet chocolate chips, 2/3 cups unsalted butter
Into the bowl with the butter chocolate mixture, add the brown sugar and the white sugar. Stir for 1-2 minutes to combine.
1/2 cups dark brown sugar, 1/2 cup white sugar
Add in the oil. With a whisk, mix until smooth and well incorporated.
1/4 cup oil
*The mixture should be warm at this point, and not hot. If it's hot, allow it to cool for 5 minutes before doing this step.* Add the eggs and vanilla in. Continue whisking until smooth, about 2-3 minutes.
1 tbsp vanilla, 3 eggs
Add the dry ingredients into the wet. Make sure to sift the cocoa powder. With a spatula, stir to combine. A thick brownie batter will form. Don't over-mix.
Mix in the chocolate chips a few times until well incorporated.
3/4 cups semi-sweet chocolate chips
Scoop the brownie batter into each liner, they should be full. Add extra chocolate chips on top if desired.
Bake for 25-35 minutes. If you want gooey middles, check after 25 minutes. For more chewier cups, bake for 30-35 minutes. I baked mine for 27 minutes exactly.
When they are ready, remove from your oven and allow them to cool. They may sink a bit, but this is normal with these brownies. When they are almost completely cooled, gently run a knife around the bottom of the muffins to pop them out. Enjoy!!