Brown the butter: In a light‑colored saucepan over medium heat, melt butter and stir continuously for 5–6 minutes until it foams and the milk solids turn golden brown with a nutty aroma. Immediately pour into a heatproof bowl and cool for 45 minutes until solidified but soft.

Cream sugars & butter: Beat browned butter with granulated and light brown sugars until fluffy using a hand or stand mixer.

Add wet ingredients: Mix in egg and vanilla until fully combined, scraping bowl as needed.

Combine dry ingredients: In a separate bowl, whisk flour, baking soda, and salt. Add gradually to wet mixture, stirring until a soft, sticky dough forms.

Chill dough: Cover and refrigerate for at least 1 hour or overnight for best texture.

Shape cookies: Preheat oven to 350°F (175°C). Line baking sheets with parchment. Scoop 2‑tbsp dough portions, roll into balls, and coat in sanding sugar.

Bake: Arrange 3 inches apart and bake 11–13 minutes, until edges are golden brown and centers set. Cool 5 minutes before transferring to a rack.