In a large mixing bowl, beat the softened butter and granulated sugar until light and fluffy. Add the egg yolk and mix until fully incorporated.

Add the flour and baking powder directly to the bowl. Mix just until a soft dough forms. Do not overmix.

Scoop tablespoon-sized portions of dough and roll into balls. Place on a parchment-lined tray. Press several candy-coated chocolates gently into the top of each dough ball.

Transfer the tray to the freezer and freeze for at least 1 hour, or until the dough balls are firm.

Preheat the oven to 350°F (175°C). Place frozen dough balls on a parchment-lined baking sheet, spacing them slightly apart.

Bake for 10–12 minutes, until the edges are set and the centers remain soft.

Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes. If using, sprinkle with colorful sprinkles while still slightly warm. Transfer to a wire rack to cool completely.