Brown Butter Walnut Cookies with Rosemary and Lemon

These bakery-style cookies balance nutty, caramelized brown butter — deeply infused with whole rosemary sprigs — with toasty walnuts, bright lemon zest, and an all-brown-sugar base that drives maximum chew. Walnuts bring a slightly more bitter, earthy character than pecans, complementing the rosemary and lemon beautifully. Scaling up to a generous 3-tablespoon scoop and leaning on extra egg yolks keeps the centers thick, fudgy, and rich, while an overnight chill ensures the dough bakes up tall rather than spreading thin. The dough comes together in one bowl with no mixer required.

Ingredients

• unsalted butter – 9 tablespoons (1 stick + 1 tablespoon)
• fresh rosemary sprigs (for infusing butter) – 2 sprigs
• light brown sugar, packed – scant 1 cup
• large whole egg – 1 egg
• large egg yolks (whites reserved for another use) – 2 yolks
• pure vanilla extract – 1 1/2 teaspoons
• lemons, zested (juice saved for another use) – 1 to 2 lemons (about 1 1/2 teaspoons zest)
• finely minced fresh rosemary leaves (optional, for texture and visual flecks) – 1/4 teaspoon
• all-purpose flour – 1 1/2 cups
• baking soda – a generous 1/4 teaspoon
• kosher salt – 3/4 teaspoon
• walnuts, toasted and roughly chopped – 1 cup + 2 tablespoons

Instructions

1. Brown the butter: add the butter and 2 whole fresh rosemary sprigs to a small, light-colored saucepan over medium heat. Stir occasionally as it melts. Once it foams, continue cooking and swirling until the foam subsides, the milk solids turn a deep golden brown, and it smells nutty and fragrant — about 4 to 5 minutes. The whole sprigs allow the hot fat to extract the rosemary's fat-soluble aromatic oils far more efficiently than minced leaves ever could. Remove and discard the rosemary sprigs, then immediately pour the butter (including all the browned milk solids) into a medium mixing bowl. Let it cool for 10 minutes. You want it liquid but no longer hot to the touch.
2. Whisk the light brown sugar into the cooled brown butter until smooth and combined. Add the whole egg, the 2 egg yolks, vanilla extract, and lemon zest. If using, add the optional 1/4 teaspoon minced rosemary leaves for texture and flecks. Whisk vigorously for about 60 seconds until the mixture looks slightly lighter and cohesive.
3. Add the flour, baking soda, and salt directly to the bowl. Switch to a rubber spatula and stir until just combined and no dry streaks remain — don't overmix. Fold in the toasted chopped walnuts.
4. Cover the bowl with plastic wrap and refrigerate the dough for at least 1 hour — overnight (up to 24 hours) is strongly recommended for the thickest, chewiest result and the most developed flavor. Meanwhile, when you're ready to bake, preheat the oven to 375°F / 190°C (convection: 350°F / 175°C) and line two baking sheets with parchment paper.
5. Scoop the dough into balls of about 3 tablespoons each (a #24 cookie scoop works well, roughly 2.5 oz / 70g per ball), spacing them about 3 inches apart on the prepared sheets — you will likely need two baking sheets or bake in two batches. You should get 10 to 12 cookies. Do not flatten the balls; leaving them tall and domed helps the centers stay thick and chewy.
6. Bake for 13 to 15 minutes, until the edges are set and deeply golden but the centers still look noticeably underdone, glossy, and soft — this is correct; do not overbake. Remove from the oven and let the cookies cool on the sheet for at least 8 to 10 minutes before transferring. They will look underset when they come out but will firm up into thick, chewy bakery-style cookies as they cool.