How to Make It
Heat oven to 350°F. Coat an 8-inch square baking pan with nonstick spray. Line the pan with 2 criss-crossed pieces of parchment paper, leaving an overhang on all sides; coat the parchment with nonstick spray.
In a medium bowl, whisk together the cocoa powder, flour, and salt.
Melt the butter in a medium saucepan over medium-low heat (or in the microwave). Remove from heat and mix in the granulated sugar, brown sugar, oil, and vanilla. One at a time, mix in the eggs and egg yolk; add cocoa powder mixture and stir until just combined. Fold in the chocolate chips.
Spread the batter in the prepared pan and bake until a toothpick inserted in the edges of the brownies comes out clean, 30 to 34 minutes. Cool completely in the pan.
Holding both sides of the paper overhang, lift the brownies out of the pan, transfer to a cutting board, and cut into 16 squares. Store the brownies in an airtight container at room temperature for up to 5 days.