In a large mixing bowl, combine the melted butter, granulated sugar, and brown sugar. Whisk until smooth and creamy.

Add in the egg and vanilla extract, whisking until fully combined.

In a separate bowl, whisk together the flour, baking soda, baking powder, and fine sea salt. Gradually fold this into the wet ingredients until just combined.

Gently fold in the colorful Christmas sprinkles. Cover the bowl and chill in the refrigerator for 30 minutes.

Preheat the oven to 350°F (177°C) and line baking sheets with parchment paper.

Scoop the chilled dough onto the baking sheets, spacing them about 3-4 inches apart.

Bake for 9-11 minutes, until edges are golden and centers are slightly soft. Optionally, press more sprinkles on top right after baking.

Let cool on baking sheets for 5 minutes before transferring to a wire rack to cool completely.