Step 1

Preheat the oven to 180°C/350°F (160°C fan-forced). Grease a 20 cm/8" square pan with butter and line with baking paper (parchment paper).

Step 2

Toast walnuts - Spread the walnuts on a tray and roast for 5 minutes. Remove from the oven and cool.

Step 3

Browned butter (don't skip this step): Place the butter in a silver (not black) saucepan over medium high heat. Once melted, lower the heat to medium. Simmering gently for 3 to 4 minutes, stirring every now and then (it will go foamy), until it smells nutty and you see little golden specks in the butter. Immediately pour the butter and all the golden bits into a bowl.

Step 4

Batter: Add the sugar into the hot butter and mix to combine using a wooden spoon. Leave to cool for 3 minutes. Add the egg and vanilla, mix until combined. Add the flour and salt, and mix to combine. It will be very thick, almost like roll-able cookie dough. Add the chocolate chips and walnuts and mix through.

Step 5

Bake: Scrape into the prepared pan, spread and smooth the surface (I use my hands). Bake for 25 minutes or until the edges are lightly tinged with gold and the surface has a paper thin "crackly" layer.

Step 6

Rest in the pan for 10 minutes before lifting onto a cutting board. Cool for at least another 10 minutes (else it's still a bit too soft and smeary), sprinkle with salt flakes (if using). Cut into 16 squares or 9 giant squares, then devour!