Frosting and glaze offer easy ways to get sprinkles to stick to already baked cookies. You can also cover cookies with sprinkles before baking, but they will melt and turn into colorful icing.
Frost or glaze the cooled cookie with homemade or store-bought icing.
Immediately add the sprinkles. They don't stick to frosting that's stiffened from sitting out at room temperature.
Press the sprinkles lightly with the flats of your fingers into the frosting, especially if you plan on transporting the cookies.
Only frost the cookies after they've cooled to room temperature. The ingredients in the icing or glaze may melt and spread. The sprinkles may melt, too.
Drizzle the cookies with melted chocolate and then coat with sprinkles for a flavor alternative. As the chocolate hardens at room temperature, the sprinkles will remain adhered. Alternatively, dip the cookie into melted chocolate and top with the sprinkles.
Beat together the whites of 2 pasteurized eggs and 1/4 teaspoon of water.
Use a pastry brush to paint a light film of the egg white mixture on the cookies.
Shake the sprinkles on immediately, before the clear glaze has time to dry, so they stick. You won't taste or see the glaze when it dries.