Preheat your oven to 180°C (conventional) or 160°C (fan). Line a muffin tin with paper cupcake cases.

In a large mixing bowl, combine room temperature butter, banana milkshake powder, all-purpose flour, and eggs. Mix for 2-3 minutes until smooth.

Spoon the batter into the lined cupcake cases, filling each about two-thirds full.

Bake in the preheated oven for 25-30 minutes until golden brown and springing back when touched.

Remove from the oven and let cool for 5-10 minutes in the tin before transferring to a wire rack.

For the buttercream, cream together softened butter and icing sugar for 3-5 minutes until smooth. Add milk if too thick.

Frost cooled cupcakes with the buttercream, covering generously.

Decorate with toppings like foam bananas or colorful sprinkles.