Preheat your oven to 350°F (175°C) and grease a muffin tin or line it with cupcake liners.

In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt.

In another bowl, mix the milk, melted butter, egg, and vanilla extract until well combined.

Gradually add the wet ingredients to the dry ingredients, stirring until a smooth batter forms.

Divide the batter into separate bowls, depending on how many colors you'd like to use, and add a few drops of food coloring to each bowl. Mix until the colors are evenly blended.

Using a spoon or piping bag, drop small 'dots' of each colored batter into the muffin tin, layering them to create a polka dot or marbled effect.

Bake for 15-18 minutes, or until a toothpick inserted into the center of the cakes comes out clean.

Remove the cakes from the oven and let them cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.

Optionally dust the cakes with powdered sugar before serving.