In a mixing bowl, whisk together the sugar and cooled melted butter until smooth and combined. Add the egg and vanilla extract, then whisk again until fully incorporated.
Mix in the baking soda, baking powder, corn starch, and salt until evenly distributed.
Add half of the flour and fold it into the wet mixture, then add the remaining flour and fold until a dough forms. Gently fold in the sprinkles, ensuring they are evenly distributed throughout the dough.
Cover the dough with plastic wrap, ensuring the wrap touches the surface, and refrigerate for 20 to 30 minutes.
Preheat your oven to 170°C (338°F) and line a baking tray with parchment paper.
Scoop out 1 1/2 tablespoons (about 30g) of dough per cookie. Roll into balls, dip in extra sprinkles, and place them on the prepared baking tray, spacing them evenly apart.
Bake in the preheated oven for 10-12 minutes, or until the edges are just set. The centers should still look slightly soft.
Remove from the oven and let the cookies cool on the baking tray for a few minutes before transferring them to a wire rack to cool completely.
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Notes
Nutrition info is estimated and may vary based on ingredients and portions. For the most accurate details, consider using a nutrition tool or checking our full Nutrition Information Disclaimer.