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• Browning the butter is a Maillard reaction on milk solids. Butter is about 16% water and 1–2% milk protein and sugar. Cooked past the point where the water boils off, those solids toast and produce nutty, caramel aromatics that no amount of vanilla imitates. See baking fats.
• Browned butter has lost its water, so put some back. Two tablespoons of milk or an extra yolk, or the cookie bakes dry and crumbly. This is the step most recipes omit and most home bakers notice as "drier than expected".
• Cool the browned butter to room temperature before creaming. Hot butter melts the sugar and the cookie spreads flat.
• Toffee, not caramel. Hard toffee pieces melt into pools that reset crisp; soft caramel stays liquid and leaks.
• Flaky salt goes on as they come out, not before — it dissolves in the oven.

Makes about 20 large cookies.

• 225 g unsalted butter
• 250 g dark brown sugar
• 100 g granulated sugar
• 1 egg plus 1 yolk
• 2 tbsp milk
• 2 tsp vanilla — see Pure vanilla extract
• 310 g all-purpose flour
• 5 g baking soda
• 6 g fine salt
• 200 g hard toffee, chopped, or toffee bits
• 150 g dark chocolate, chopped — see Chocolates
• flaky salt, to finish

Brown the butter in a light-coloured pan over medium heat: it will foam, then quieten, then the solids at the bottom will turn amber and smell of hazelnut. That is about six minutes. Scrape everything, solids included, into a bowl and cool to room temperature — 30 minutes, or 10 in the fridge with stirring.

Beat the cooled butter with both sugars, then the egg, yolk, milk and vanilla, two minutes.

Fold in the flour, soda and salt, then the toffee and chocolate.

Chill at least two hours, ideally overnight — see the rested-dough argument on chocolate chip cookies.

Scoop 70 g balls, space widely, and bake 180 °C / 350 °F for 12–14 minutes, until the edges are set and the centres puffed and pale. Rap the tray on the bench once as they come out to set the ripples, and finish with flaky salt.

• Make toffee from scratch if you want the bakery version: 200 g sugar and 100 g butter cooked to 150 °C, poured thin, cooled, and smashed.
• The browned butter smell is the doneness cue. Colour lags behind aroma by about thirty seconds and a black-bottomed pan hides it entirely.
• Keeps four days and freezes well as scooped dough.

Method and theory: Cookie recipes · cookies · baking fats · sugar in baking

Nearby: chocolate chip cookies · chocolate tahini cookies · cowboy cookies