Step 1

Preheat oven to 180°C/350°F (160°C fan). Lightly grease then line three baking trays with paper.

Step 2

Brown butter - Melt butter in a small silver pan or saucepan over medium heat (Note 2). Leave to simmer on medium heat for 3 to 5 minutes, stirring every now and then, until (when you push foam aside) you see little golden-brown bits. Immediately pour into a bowl (including the golden bits) and set aside to cool for 5 minutes.

Step 3

Chop choc - Cut the chocolate into 1cm /1/4" pieces. Transfer the chunks into a bowl and leave the fine chocolate dust behind for another purpose (makes cookies speckled, Note 1).

Step 4

Mix dough - Whisk flour, oats, baking soda, and salt in a large bowl. Add sugar to the brown butter and whisk (it might not combine fully). Add egg and vanilla, whisk until smooth.

Step 5

Finish dough - Add dry ingredients into the egg mixture. Mix with a wooden spoon until the flour is almost mixed in. Add chocolate, and stir until mixed through and you can no longer see flour. Set aside for 5 minutes to let the mixture firm up a bit.

Step 6

Cookies - Scoop a heaped tablespoon of dough onto the tray, 5 cm / 2 " apart. (I use a size 40 cookie scoop, makes 22 cookies) Flatten to 8 mm / 1/3" thick, reshaping sides if needed if they split/go wonky.

Step 7

Bake - Bake 2 trays for 11 minutes, switching shelves and rotating the tray at the 7 minute mark, or until the surface is light golden. For 1 tray, bake 10 minutes, rotating the tray at the 6 minute mark.

Step 8

Cool on the tray for 10 minutes, then transfer onto a cooling rack to fully cool. (A sprinkle of salt flakes wouldn't go astray!)