Preheat your oven to 350°F (175°C). Grease a large sheet pan, usually a 15×10-inch.

In a mixing bowl, combine the flour, sugar, cocoa powder, baking soda, and salt.

In a saucepan over medium heat, stir together the Dr. Pepper and vegetable oil until just combined.

Pour the heated mixture over the dry ingredients, mixing until smooth.

Add the eggs, buttermilk, and vanilla extract to the batter and whisk until well-blended.

Pour the cake batter into the prepared sheet pan, smoothing it out to ensure an even surface.

Bake for about 20-25 minutes, or until a toothpick inserted into the center comes out clean.

Remove from the oven and let it cool completely on a wire rack.

While the cake cools, prepare the frosting by combining powdered sugar, cocoa powder, melted butter, and a splash of Dr. Pepper.

Mix until achieving a smooth consistency that’s easy to spread.

Pour the frosting over the cooled cake, letting it cascade over the edges.