Delicious M&M Surprise Cupcakes with Rainbow Frosting

Ingredients:

For the Cupcakes:
105g (3/4 cup) Plain Flour
40g (1/2 cup) Cocoa Powder
1/2 tsp Baking Soda
1/2 tsp Baking Powder
100g (1/2 cup) Caster Sugar
45g (1/4 cup) Brown Sugar
2 Large Eggs
115g (1/2 cup or 1 stick) Unsalted Butter, softened
1 tsp Vanilla Extract
120 ml (1/2 cup) Buttermilk
1 cup Mini M&Ms for filling
For the Frosting:
115g (1/2 cup or 1 stick) Unsalted Butter, softened
500g (4 cups) Icing or Powdered Sugar
2-3 tbsp Milk
Food Colouring in chosen colors