Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a large mixing bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Whisk together until well mixed.
Add the egg, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat on medium speed for about 2 minutes until smooth.
Carefully stir in the boiling water until fully combined; the batter will be thin.
Pour the batter into the prepared muffin tin, filling each liner about two-thirds full.
Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cupcakes to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
For the frosting, beat the softened butter in a mixing bowl until creamy.
Gradually add the powdered sugar, mixing on low speed until combined.
Add the heavy cream and vanilla extract, then beat on high speed for about 3 minutes until fluffy.
Divide the frosting into two bowls. Color one bowl with red food coloring and the other with blue food coloring.
Use a piping bag fitted with a star tip to frost the cooled cupcakes, alternating between red and blue frosting.
Top each cupcake with red and blue sprinkles for a festive touch.