Start by browning the butter. In a medium-sized saucepan add the butter (which has been at room temperature for 20-30 minutes) and melt in on medium heat swirling the saucepan constantly.
Once the butter has melted, the butter will start to sizzle up and a layer of foam will cover the entire pan. Once you cant see the butter, remove it from the heat and transfer the brown butter to a big mixing bowl to cool to room temperature.
Add the brown sugar, sugar, salt, and vanilla extract to the bowl with the brown butter and mix with a whisk until well combined.
Add the egg and egg yolk and mix well.
Sift the flour and add the baking soda and gently mix until the mixture is almost combined.
Chop dark chocolate or semisweet chocolate bars into chunks and add the chunks into the cookie dough mixture.
Fold the mixture with a spatula until just combined, cover the bowl with plastic wrap, and let the dough rest in the fridge for at least an hour. We let the dough rest in the fridge overnight.
Use a cookies scoop to scoop out the cookies or scoop the cookies with a regular tablespoon, 1 ½ tablespoon at a time.
Place the cookie dough balls onto a parchment paper-lined baking sheet, top with more chocolate chunks, and bake in a 180c (350f) preheated oven for 9-11 minutes.
Top each cookie with flaky salt and serve next to a cup of milk for the best experience!