Tried and loved this recipe? Please leave a 5-star review below! Your reviews mean a lot to me, so if you've got any questions, please let me know in a comment.
Preheat oven to 350 degrees and line a 9x9 inch baking pan with parchment paper.
Whisk brownie mix, oil, eggs, Dr Pepper, and vanilla until smooth and glossy, then spread evenly in the pan.
Bake 30 to 35 minutes, until a toothpick comes out with a few moist crumbs. Cool slightly.
Combine Dr Pepper, butter, cocoa powder, and sugar in a small saucepan. Boil gently over medium heat, whisking constantly, for 3 to 4 minutes until slightly thickened.
Off the heat, stir in vanilla and a pinch of salt.
Slice into squares, drizzle with warm sauce, and serve with ice cream if desired.
Notes
Don't overbake. The brownies continue to set as they cool, so pull them once the toothpick shows a few moist crumbs rather than coming out fully clean.
Dr Pepper adds a subtle caramel-cherry note that makes boxed brownie mix taste homemade. Cherry Dr Pepper works too, for an even stronger cherry flavor.
Drizzle the sauce while it's still warm for the glossiest finish. If it cools and thickens too much, spread it over the brownies like frosting instead.
Stir ½ cup chopped pecans or walnuts into the batter for a nutty version.
Store brownies without sauce in an airtight container up to 4 days, or freeze up to 3 months. Keep the sauce refrigerated up to 1 week and reheat gently before using.