Preheat the oven to 325°F (160°C) and line a baking sheet with parchment paper.

Beat softened butter in a large bowl for 3–4 minutes until light and fluffy. Mix in powdered sugar and vanilla until smooth.

Sift together flour and cornstarch, then gradually add to the butter mixture, blending until just combined. If the dough feels too soft, chill for 10–15 minutes.

Drop tablespoonfuls of dough onto the sheet or pipe rosettes with a star tip. Add sprinkles if desired.

Bake for 12–15 minutes until the edges are barely golden. Cool on the pan for 5 minutes, then transfer to a wire rack to finish cooling.