In a large bowl, beat the softened butter and sugar together until it’s light and fluffy. Add the egg yolk and mix until everything is smooth.
Stir in the flour and baking powder. Mix just until it forms a soft dough, don’t overmix, or your cookies will be tough.
Scoop out tablespoon-sized pieces of dough and roll them into balls. Place them on a parchment-lined tray. Gently press a few candy-coated chocolates into the top of each ball for that classic Easter look.
Pop the tray in the freezer for at least 1 hour. The dough balls should be firm before baking.
Preheat your oven to 350°F (175°C). Arrange frozen dough balls on a parchment-lined baking sheet, leaving a little space between them. Bake for 10–12 minutes. The edges will be set, but the centers will stay soft and chewy.
Let the cookies cool on the baking sheet for 5 minutes. If you want, sprinkle on some colorful sprinkles while they’re still slightly warm. Then, transfer them to a wire rack to cool completely.