Brown-Butter Chocolate Chip Cookies

Brown the butter. Melt the butter in a light-coloured saucepan over medium heat, swirling constantly, for 5-7 minutes, until it foams, then goes quiet and the milk solids turn amber with a distinctly nutty smell. A light-coloured pan makes it far easier to see the colour change happening, since a dark pan can hide it until the butter burns. As soon as it smells nutty, pour it straight into a heatproof bowl, scraping in all the browned bits from the base of the pan.

Cool the brown butter. Whisk the ice cube into the hot butter straight away, which replaces the water that boiled off while browning. Chill the butter, stirring occasionally, for about 20 minutes, until it's cool and about the texture of soft butter. Skipping this step and using the butter while still hot would cook the eggs when you combine them later.

Whip eggs and sugar. Whisk the egg, egg yolk, both sugars and the vanilla on medium-high speed for 3-5 minutes, until the mixture turns pale and falls in a thick, ribbon-like trail off the whisk. Whipping the sugar this thoroughly into the eggs is what gives these cookies their crisp edges and toffee-like chew once baked. Don't rush this stage, since an underwhipped mixture gives a flatter, less chewy cookie.

Combine and fold in chocolate. Beat in the cooled brown butter until smooth, then fold in the flour, bicarbonate of soda and salt just until no streaks of flour remain. Fold in the chopped chocolate chunks and shards last, mixing only enough to distribute them evenly. Overmixing once the flour is in can make the cookies tough rather than tender.

Chill the dough. Cover the dough and chill for at least 1 hour, ideally 24 hours and up to 72 hours. The longer rest lets the flour fully hydrate and allows deeper, more butterscotch-like flavours to develop, while also firming the dough enough to spread less in the oven. This is the step that separates an ordinary cookie from a genuinely chewy, flavourful one.

Heat the oven. Heat the oven to 175°C (155°C fan) for at least 20 minutes, with a shelf in the middle. Scoop the chilled dough into 45 g balls, spacing them 7 cm apart, six to a tray. Giving the oven the full preheating time means the cookie edges set and hold their shape as soon as they go in.

Bake one tray at a time. Bake one tray at a time for 11-13 minutes, until the edges look golden and set but the centres still look puffy and slightly underdone. Baking a single tray at a time means the heat is consistent across every cookie rather than being shared between two trays. The centres will finish cooking as the cookies cool, so don't wait for them to look fully baked in the oven.

Finish and cool. Sprinkle with flaky sea salt as soon as the cookies come out of the oven, then leave them on the tray for 5-10 minutes before moving them. This resting time lets carryover heat finish setting the centres without the cookies needing any longer in the oven. Transfer to a wire rack to cool. Makes about 24 cookies.