Preheat your oven to 350°F (175°C) and line a cupcake pan with paper liners.

In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt until well combined.

In another bowl, mix the buttermilk, vegetable oil, eggs, and vanilla extract. Gradually add this mixture to the dry ingredients and stir until just combined.

Carefully stir in the boiling water until the batter is smooth.

Divide the batter evenly into two bowls. Add red food coloring to one bowl and blue food coloring to the other, mixing until the desired colors are achieved.

Spoon alternating dollops of red and blue batter into each cupcake liner, creating a marbled effect.

Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean. Allow the cupcakes to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.

While the cupcakes cool, prepare the frosting. In a large bowl, beat the softened butter until creamy. Gradually add the powdered sugar, heavy cream, and vanilla extract, beating until smooth and fluffy.

Frost the cooled cupcakes with the buttercream frosting and decorate with red, white, and blue sprinkles.