Ingredients

• 170 g unsalted butterplus extra for the skillet
• 160 g soft light brown sugar
• 80 g caster sugar
• 1 egg, plus 1 extra yolklarge, at room temperature
• 1 tsp vanilla extract
• 240 g plain flour
• 1/2 tsp bicarbonate of soda
• 1/2 tsp fine sea salt
• 180 g dark chocolatechopped from a bar; chips are built to hold their shape, and you want pools
• 100 g blanched hazelnutswhole, to toast yourself
• 500 ml vanilla ice creamto serve
• 1/2 tsp flaky sea saltto finish

Method

1. 01

   Toast the hazelnuts

   Heat the oven to 180C fan / 200C conventional. Spread the hazelnuts on a tray and toast for 9-11 minutes, shaking once, until they smell strongly nutty and are golden through to the centre. Break one open to check. Cool for 10 minutes, then chop roughly so you have a mix of halves and rubble. Leave the oven on.

   100 g blanched hazelnuts

   Maple on the hot hazelnutsA teaspoon tossed through before chopping. It costs nothing and lacquers them.

2. 02

   Brown the butter

   Melt the butter in a light-coloured saucepan over medium heat. It will foam, then quieten as the water cooks off; swirl continuously and watch the milk solids on the base. At 5-6 minutes they turn deep amber and the smell goes from buttery to nutty and toffee-like. Pour it immediately into a large mixing bowl, scraping every brown speck in with it.

   170 g unsalted butter

3. 03

   Let it cool

   Leave the brown butter for 10-15 minutes, until it is no warmer than a bath. This is not optional and it is not a rest step. Hot butter melts the sugar into syrup and cooks the egg, and you will end up with a greasy, flat, crisp biscuit instead of a thick chewy cookie. Test it with a fingertip before you go on.

4. 04

   Whisk the wet mixture

   Whisk the brown sugar and caster sugar into the cooled butter for about a minute until it looks like wet sand and no longer grainy on the whisk. Add the whole egg, the extra yolk and the 1 tsp vanilla and whisk hard for another minute, until the mixture has lightened a shade and thickened enough to ribbon briefly off the whisk. That extra yolk is doing the work of making it chewy rather than cakey.

   160 g soft light brown sugar · 80 g caster sugar

5. 05

   Fold in the dry ingredients

   Add the flour, bicarbonate of soda and fine salt and fold with a spatula just until the last streak of flour disappears. No more. Overworked dough develops gluten and bakes tough. Then fold through about three-quarters of the chopped chocolate and hazelnuts.

   240 g plain flour · 1/2 tsp bicarbonate of soda · 1/2 tsp fine sea salt

6. 06

   Press into the skillet

   Butter a 25 cm cast-iron skillet. Tip the dough in and press it out to the edges with your fingertips, leaving the surface uneven and craggy rather than smooth. The ridges brown and the valleys stay soft. Push the reserved chocolate shards and hazelnuts into the top so they are visible.

7. 07

   Bake until the middle looks underdone

   Bake at 180C fan for 18-24 minutes. The edges should be deep golden and visibly set and pulling from the skillet; the centre 8 cm should still look soft, pale and slightly wet. It will carry on cooking in the hot pan after it comes out, and a skillet cookie baked until the middle looks done in the oven is a dry one on the plate. If in doubt, take it out a minute early.

8. 08

   Rest, salt and serve

   Rest 5 minutes in the pan. Long enough for the centre to firm into a fudgy scoop, short enough that the chocolate is still molten. Scatter with flaky sea salt, put two or three scoops of vanilla ice cream straight into the middle and take the whole skillet to the table with spoons. Warn everyone the pan is hot.

   Rest the dough if you canChilled in the skillet for a day or two, baked from cold with a few minutes more, it turns caramel.

   Two chocolates beat oneSeventy per cent for bitterness, milk for the molten pools. Chopped together.