Brown the butter: Place the 170 g unsalted butter in a medium light-colored saucepan over medium heat. Melt, then continue to cook, stirring frequently, until it foams and then begins to turn golden-brown with nutty aroma (3–6 minutes). Remove from heat and immediately transfer to a heatproof bowl to stop cooking. Why: Browning develops Maillard and caramelized milk solids that add deep toffee and nutty notes — a simple flavor upgrade that reads as 'chef-made.' Stopping the cooking prevents burning.

Cool slightly and add oil: Let the browned butter cool 3–5 minutes so it's warm but not hot, then whisk in 30 g neutral oil. Why: The oil keeps the cookies extra chewy by inhibiting full butter recrystallization and helps the dough spread slightly for thin, crisper edges while preserving a soft center.

Combine sugars and wet ingredients: In a large mixing bowl, whisk together 100 g granulated sugar and 150 g packed brown sugar. Add the warm browned-butter/oil mixture and whisk until smooth and slightly glossy. Why: Mixing sugar with warm fat helps dissolve some sugar crystals and meld flavors — contributing to a silkier dough and more even browning.

Add eggs and milk: Add 2 large eggs (room temperature) one at a time, whisking just until incorporated, then stir in 60 g whole milk and 10 g vanilla extract. Why: Eggs provide structure and moisture; adding them one at a time ensures even emulsification. A small splash of milk increases tenderness and keeps the dough pliable, which helps achieve a fudgy crumb.

Dry ingredients: In a separate bowl, whisk together 300 g all-purpose flour, 5 g baking soda, and 5 g fine sea salt. Why: Whisking the dry ingredients evenly distributes leavening and salt so the cookies rise uniformly and flavor is balanced throughout.

Combine wet and dry: Using a sturdy spatula, fold the dry mix into the wet in two additions. Fold just until you no longer see streaks of flour — do not overmix. Why: Overmixing develops gluten and makes cookies tough; gentle folding yields a tender but structured crumb.

Fold in chocolate: Gently fold in 170 g semisweet chocolate chips until evenly distributed. Why: Fold at the end to avoid breaking chips and to maintain dough texture.

Chill the dough (optional but recommended): Cover the bowl and refrigerate for 30–60 minutes. Why: Chilling firms the fat so the cookies spread less in the oven, concentrates flavors, and improves texture — 30 minutes is enough for better results; longer (up to 24 hours) deepens flavor.

Preheat and portion: Preheat oven to 180°C/350°F. Line two baking sheets with parchment paper or a silicone mat. Using a 60–65 g ice cream scoop or two spoons, portion dough into 18 equal balls about 2 tbsp each and place them 2–3 inches apart on the sheet. Why: Uniform portions ensure even baking and consistent chew between cookies.

Top and flatten slightly: If desired, press a few extra chocolate chips and a light sprinkle of flaky sea salt onto each ball, then gently press each ball to slightly flatten (about 1/2" thick). Why: Adding chips on top makes the cookie photogenic and the salt brightens and balances the sweetness.

Bake: Bake in the preheated oven 10–12 minutes, rotating the pan halfway through. Pull them when edges are golden-brown and centers still look slightly underbaked and glossy. Why: Pulling slightly early ensures a chewy, fudgy center — cookies continue cooking on the sheet from residual heat.

Cool: Let cookies rest on the baking sheet 5 minutes, then transfer to a wire rack to cool completely. Why: The brief rest allows structure to set so they don't break when moved; cooling on a rack prevents sogginess from trapped steam.