Brown the butter. Melt the butter in a light-coloured saucepan over medium heat. It will hiss and foam, then settle into a quiet sizzle. Keep swirling until the milk solids at the bottom turn the colour of hazelnut skins and the kitchen smells nutty and toasted, about 5–7 minutes. Pour it into a large bowl straight away so it stops cooking, then leave it for 10 minutes until it is warm rather than hot.

Whisk the sugars in. Add both sugars to the warm butter and whisk for a full minute. The mixture should look glossy, thick, and the colour of wet sand, with no dry sugar left at the bottom of the bowl.

Beat in the eggs and vanilla. Add the egg, yolk, and vanilla, then beat hard for 2 minutes. The batter will lighten to a pale toffee shade and fall from the whisk in a slow ribbon rather than a thin stream.

Fold in the dry ingredients. Tip in the flour, bicarbonate of soda, fine salt, and cinnamon if using. Fold with a spatula just until the last streaks of flour disappear. Stop the moment it comes together; overmixing develops gluten and gives you tough cookies.

Add the chocolate. Fold through the chocolate chips until they are evenly scattered. The dough will be soft and slightly sticky, which is exactly right.

Chill briefly. Cover the bowl and rest the dough in the fridge for 20 minutes. This firms the butter back up so the cookies spread slowly rather than flooding the tray.

Heat the oven and scoop. Preheat the oven to 180°C (160°C fan, gas mark 4) and line two baking trays with parchment. Scoop golf-ball-sized mounds, about 55 g each, and space them 8 cm apart, six to a tray.

Bake. Bake for 11–12 minutes. The edges should be set and golden-brown while the centres still look slightly underdone and puffed. They will smell of caramel and toasted nuts as they come out.

Finish and cool. Sprinkle each cookie with a few flakes of sea salt and leave them on the tray for 5 minutes. They will deflate slightly and wrinkle at the edges, which is the sign of a chewy centre. Move them to a wire rack to cool completely.