Preheat the Oven:
Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking pan or line it with parchment paper.

Prepare the Brownie Batter:
In a medium saucepan, melt the butter over medium heat. Remove from heat and stir in the granulated sugar until well combined.

Mix the Wet Ingredients:
In a large mixing bowl, whisk together the eggs and vanilla extract. Gradually add the butter and sugar mixture, whisking constantly until smooth.

Add Dry Ingredients:
In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Gradually add the dry ingredients into the wet mixture, stirring until fully combined.

Add Dr. Pepper Soda:
Slowly pour in the Dr. Pepper soda and stir until smooth and the batter is well mixed.

Bake the Brownies:
Pour the brownie batter into the prepared pan. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Allow the brownies to cool completely.

Make the Dr. Pepper Glaze:
In a small saucepan, combine the Dr. Pepper soda, butter, and cocoa powder. Bring to a simmer, stirring constantly. Remove from heat and whisk in the powdered sugar and vanilla extract until smooth.

Glaze the Brownies:
Once the brownies are cooled, pour the Dr. Pepper glaze over the brownies, spreading it evenly with a spatula.

Serve:
Slice into squares and enjoy these delicious, fudgy Dr. Pepper brownies!