Preheat oven to 350°F (convection). Beat room-temperature butter in a stand mixer or by hand for 3–5 minutes until slightly off-white.

Add granulated sugar and beat with the butter until fluffy, about 2 minutes.

Add the egg and vanilla extract, mixing until fully combined.

Add flour, baking soda, baking powder, and Halloween sprinkles. Fold until a cookie dough forms.

Use a 1/3 cup scoop (or desired size) to place a single dough ball on a tray. Bake this test cookie to check spread and oven temperature. Adjust if needed.

Place remaining dough balls on the tray, spacing evenly. Flatten slightly if desired. Bake for 12–14 minutes (for 1/3 cup scoops).

For perfectly round cookies, gently swirl a cup or bowl around each fresh cookie. Let sit on the tray for 10 minutes before removing.

Beat butter until slightly off-white. Add powdered sugar and heavy cream, then vanilla extract. Whip until fluffy.

Frost the cooled cookies and sprinkle with Halloween sprinkles. Store in the fridge for up to 10 days or at room temperature for up to a week.