Set the butter in a small frying pan and turn the heat to medium. Let it cook as it sputters and bubbles until it goes quiet. Remove it from the heat and pour into a heatproof bowl, making sure to scrape the brown bits into the bowl. You can measure it at this point, you’ll need 85-90grams for the cookie dough. If you have less, brown some more butter and reserve extra for another use. If you have more, reserve for another use.
Let the butter cool in a bowl until it’s thick and creamy. You can do this at room temperature for a few hours or use the fridge/freezer to speed up the process.
Preheat the oven to 350 F.
In a mixing bowl, add the butter, sugar vanilla and sea salt and whisk for a full minute.
Add the egg yolks and sour cream and whisk for another full minute or two until it’s airy and creamy.
Add the baking soda and flour and mix with a rubber spatula.
Fold in the chocolate.
Portion dough onto a cookie sheet lined with parchment paper into mounds that are 2 tablespoons each. Roll them between your palms to smooth out the tops. Let sit at room temp for 10 minutes.
Bake for 12 minutes, until golden and dark on the edges.