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1
Preheat oven to 350 degrees F (175 degrees C). Line a 9-inch baking pan with parchment paper; grease parchment paper with cooking spray.
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2
Whisk flour, sugar, baking powder, baking soda, and salt together in a bowl.
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3
Combine buttermilk, egg, butter, and vanilla extract together in a small bowl, beating to break up the egg. Add flour mixture; stir until just combined. Fold chocolate chips gently into the batter. Allow batter to rest for 5 minutes.
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4
Combine brownie mix, oil, eggs, and water in a large bowl; whisk together until smooth.
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5
Pour 1/2 cup of the brownie batter into a squeeze bottle, pastry bag with a small round tip, or large resealable plastic bag with corner snipped off. Reserve remaining batter.
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6
Heat a large nonstick skillet over medium-low heat. Drop 1/3 cup pancake batter into the skillet, shaking skillet to spread batter evenly. Drop 5 nickel-size dollops of brownie batter over the pancake; swirl using a skewer or knife edge. Cook until edges are dry, 2 to 3 minutes. Flip and cook until set on the other side, 1 to 2 minutes. Repeat with remaining batters.
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7
Pour reserved brownie batter into the prepared pan.
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8
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 28 to 30 minutes. Cool on a wire rack before slicing.
