Preheat the oven

• Preheat the oven to 175 °C and prepare a baking dish.

Make the cookie dough

• Cream the butter and sugar together until light and fluffy.
• Beat in the egg and vanilla extract.
• Mix in the flour and baking powder until a dough forms, then fold in the sprinkles.

Bake the bars

• Press the dough evenly into the baking dish.
• Bake until the edges are lightly golden and a toothpick comes out clean.

Decorate and serve

• Let the bars cool completely in the dish.
• Spread the icing over the top and finish with sprinkles.
• Cut into bars and serve.