Brown-butter chocolate-chip cookies

This is the second cookie recipe I'm trying from AmbitiousKitchen.com. These cookies are a bit more complicated than the other ones, but they are proper cookies.

These cookies have a Nutella centre, but that step can be omitted to make the plain version.


Ingredients

9/4 cup (560 ml, 335 g) plain flour sifted

variation:
replace 1 tablespoon (15 ml) or 9 g of plain flour
with 1 tablespoon (15 ml) cornflour

5/4 teaspoons (6.25 ml) baking soda
1/4 (1.25 ml) teaspoon of salt
1 cup (~227 g) unsalted butter
5/4 (~ 300 g) cup packed dark brown sugar
1/4 (~ 50 g) cup granulated sugar
1 large egg and 1 egg yolk
3/2 teaspoons vanilla extract
1 tablespoon plain yoghurt
200 g chocolate chips
Optional: Nutella (or equivalent) cooled (to be a little bit easier to handle)
Optional: Coarse sea salt for sprinkling


Directions

Sift the flour, add the baking soda and salt and whisk together.

The browning of the butter is probably the most difficult step because butter can burn easily. Have a glass bowl ready to put the butter in to cool down when it's done. Melt the butter in a saucepan over medium heat and whisk to keep it uniform. At first, the butter should begin to foam, and in a couple of minutes it will start turning brown on the bottom of the saucepan, and it will give off a nutty smell. At this point, it needs to be removed from the fire and poured into the glass bowl to cool down; otherwise, it can burn, which will make it smell bad and taste bitter.

With a mixer, beat the butter with the brown and granulated sugar until uniform. Add in the eggs, vanilla and yoghurt, and continue beating until uniform. Change to dough hooks and add in the flour mix slowly while beating on low speed until uniform. Finally, fold in the chocolate chips. The dough is now ready.

Shape and wrap the dough in cling film (shaping it into a rectangle makes it easier to equally divide the dough for the cookies). Place the dough in the refrigerator for at least two hours; overnight is even better.

When ready to bake, divide the dough into about 30-36 pieces and roll into balls. If using Nutella, flatten the ball, add 1 teaspoon of the cold Nutella in the centre and gently fold the dough around it to form a ball again. Make sure there's no Nutella coming out.

Heat the oven to 450 K (~180 deg. C). Place the cookie balls on a cookie sheet with baking paper, with at least two inches between them, and gently flatten the top a bit. Bake for 9-11 minutes or until until the edges of the cookies begin to turn golden brown. They will look underdone in the centre, but they continue to cook after you remove them from the oven. Allow to cool for a few minutes and carefully transfer to a wire rack.