Have a large heat-proof bowl handy. Slice the butter into pieces and place in a light-colored skillet. (Light colored helps you determine when the butter begins browning.) Melt the butter over medium heat, whisking occasionally. Once melted, the butter will begin to foam. Keep whisking occasionally. After 5–8 minutes, the butter will begin browning; you’ll notice lightly browned specks begin to form at the bottom of the pan and it will have a nutty aroma. See photo above for a visual. Once browned, remove from heat immediately, pour into bowl. Allow to cool for 5 minutes.

Meanwhile, whisk the flour, baking soda, and salt together in a medium bowl. Set aside.

Add the granulated sugar and brown sugar to the brown butter. Using a handheld mixer or stand mixer with paddle attachment, beat together on medium-high speed until relatively combined, about 1 minute. Beat in the egg and vanilla extract.

Pour the dry ingredients into the wet ingredients and begin beating together on low speed, slowly working up to high speed until everything is combined. The dough will be thick and a little greasy. That’s ok! Just roll into balls as best you can in the next step.

Roll the dough into balls, about 1 Tablespoon of dough each, and dip the tops into sprinkles. Place dough balls tightly together on a lined baking sheet (or a couple large plates). Loosely cover with plastic wrap and place in the refrigerator to chill for 30 minutes.

Preheat oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats. (Always recommended for cookies.)

Line chilled dough balls onto baking sheets about 3 inches apart. Bake for 12–13 minutes or until lightly browned on the sides. Remove from the oven and allow to cool on the baking sheet for 5 minutes then transfer to cooling rack to cool completely.