Set oven to 350°F (175°C) and line baking sheet with parchment.
Beat butter and sugar until fluffy.
Add egg and vanilla extract.
Whisk flour, gelatin, baking powder, and salt.
Add dry to wet ingredients.
Roll dough into 1-inch balls, flatten slightly, and add sprinkles.
Bake for 8–10 minutes until edges are set.
Rest 5 minutes, then transfer to rack to cool completely.
