Start by melting the butter and letting it cool slightly. In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth. Add the egg and vanilla extract and mix again until everything is well combined.
Stir in the baking soda and salt. Then slowly add the flour, mixing until just combined—don’t overmix or the cookies can become tough. Gently fold in the chocolate chips and sprinkles until they’re evenly spread through the dough.
Use a cookie scoop or tablespoon to form dough balls and place them on a lined baking sheet. Cover and refrigerate for at least 2 hours (or overnight for even more flavor). Chilling helps the dough firm up and prevents the cookies from spreading too much in the oven.
Preheat your oven to 350 °F (175 °C). Arrange the chilled dough balls on a baking sheet about 2 inches apart. Bake for 11–15 minutes or until the edges are golden and the centers look just set. Let them rest on the sheet for about 10 minutes before transferring to a wire rack to cool completely.