Preheat your oven to 350°F (175°C) and line a cupcake pan with liners. In a mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt until well combined.

In a separate bowl, mix the milk, egg, vegetable oil, vanilla extract, and mashed banana until smooth. Gradually combine the wet and dry ingredients, stirring gently until just mixed.

Distribute the cupcake batter evenly into the lined pan, filling each liner about three-quarters full. Bake for about 20 minutes or until the tops spring back.

Once baked, let the cupcakes cool in the pan for about 5 minutes before transferring them to a wire rack to cool completely.

In a large bowl, whip room temperature unsalted butter until light and fluffy, about 3 to 5 minutes. Gradually add the powdered sugar and heavy cream, mixing until smooth. Optionally add vanilla extract for extra flavor.

To make the ganache, place semisweet chocolate chips in a microwave-safe bowl with heavy cream. Microwave for 30 seconds, stir, and heat in 15-second intervals until smooth.

Use a piping bag fitted with a Wilton 1M tip to swirl the buttercream frosting on each cupcake. Chill the frosted cupcakes for 30 minutes, then drizzle the ganache on top.

Sprinkle with rainbow decorations and top each with a maraschino cherry.