Preheat oven to 350 degrees F. Lightly butter and line an 8-inch square baking pan with parchment paper.
Place quick oats in a mixing bowl, pour over hot water and stir. Let sit for 10 minutes.
Add cubes of butter and gently stir until butter is melted and incorporated.
Stir in sugar, and brown sugar, then whisk in the egg and vanilla.
Add flour, cocoa powder, baking soda and salt and stir until almost fully incorporated, then add ½ cup of chocolate chips and fold until evenly distributed.
Pour batter into prepared baking pan. Sprinkle with remaining chocolate chips.
Bake for 30 to 40 minutes or until a toothpick inserted near the center comes out clean.
Remove from oven and set pan on a wire rack to cool.
Use parchment paper to lift cake out of pan.
If desired, dust top with powdered sugar before slicing into squares and serving.
Cake will keep, refrigerated in an airtight container, for up to 5 days.
