Chocolate Unicorn Cake

Ingredients (21)

• + 1 ¾ cups all-purpose flour add to pantry
• + 1 cup dark cocoa powder (such as Hershey's® Special Dark), sifted add to pantry
• + 2 teaspoons baking soda add to pantry
• + 1 teaspoon baking powder add to pantry
• ✓ ¾ teaspoon salt
• + 1 cup firmly packed brown sugar add to pantry
• + ½ cup white sugar add to pantry
• + ½ cup unsalted butter, softened add to pantry
• ✓ 2 large eggs, at room temperature
• + 2 teaspoons vanilla extract add to pantry
• + 1 cup strongly brewed coffee, cooled to room temperature add to pantry
• + 1 cup sour cream add to pantry
• + 4 cups sifted powdered sugar add to pantry
• + 1 tablespoon heavy cream, or more as needed add to pantry
• + 1 drop blue food coloring, or as needed add to pantry
• + 1 drop purple food coloring, or as needed add to pantry
• + 1 tablespoon pink sprinkles, or as needed add to pantry
• + 1 (.75 ounce) tube black decorating gel add to pantry
• + 4 marshmallows, quartered add to pantry
• + 1 tablespoon pink sanding sugar, or as needed add to pantry
• + 8 birthday candles add to pantry