Tosi Microwave Brownies

The best microwave brownies, recipe by Christina Tosi.

===== Ingredients =====
-40g unsalted butter, melted
-35g buttermilk
-20g neutral oil
-1g vanilla
-1 large egg

-100g sugar
-50g cake flour
-20g cocoa powder
-2g baking powder
-2g salt

-45g chocolate chips

===== Instructions =====
1. Mix wet and dry ingredients separately, then combine. Stir in chocolate chips last.
2. Divide evenly between two mugs. Microwave starting at 1 minute, increasing in 15 second intervals until sides and top have set. Let sit for a minute to cool a bit.