Melt & Cool Butter: Melt the butter in a medium mixing bowl, until it's almost completely melted (30-60 seconds). Stir the butter until the residual heat melts it completely. Then, pop the bowl in the fridge for 12-15 minutes - we want the butter to reach an in-between state where it's not completely melted anymore, but not solid. The top of the butter may form a "crust" in the fridge - just give it a whisk to smooth things back out. If you want to be a real baking nerd like me: Check the butter's temp - it should be about 75 degrees F. 1 cup salted butter, melted
Make Cookie Dough: Add the sugars to the mixing bowl of butter, and whisk to combine. Whisk in the egg, egg yolk, and vanilla. Whisk in the milk. Stir in the dry ingredients. Add the butterscotch chips and 8 ounces of semi-sweet chocolate, reserving 2 ounces for topping the dough balls.
3/4 cup dark brown sugar, packed, 3/4 cup granulated sugar, 1 large egg, at room temperature , 1 large egg yolk, at room temperature , 2 tsp vanilla extract, 1 tbsp milk, 2 cups all-purpose flour, spooned & leveled or weighed out, 1/2 tsp baking soda, 1/2 tsp salt, 10 ounces semi-sweet chocolate, roughly chopped and divided, 1 cup butterscotch chips
Scoop Dough Balls: Scoop the dough into balls 75 grams in size. Add extra chocolate chunks to any bare spots on top of the dough balls. Chill in an airtight container in the fridge for at least 2 hours or up to 72 hours (the longer you chill - the better the flavor!)
10 ounces semi-sweet chocolate, roughly chopped and divided
Bake: Preheat your oven to 350℉. Place 4 cookie dough balls on a lined cookie sheet and bake for 10 minutes. Take the cookie sheet out and bang the pan on the top of your oven (this helps spread the cookies more, making the edges crisp and centers chewy, and adds ripples to the edges). Return to the oven for 3-4 more minutes. Remove the pan and bang the cookies one more time, then let cool on a cooling rack for as long as you can resist before digging in!
Serve & Store: Dig in while warm and gooey! Sprinkle with flaked sea salt if desired (you will, trust me). Store cooled, leftover cookies in an airtight container for 3-4 days.
flaked sea salt
Freezing Cookie Dough & Make-Ahead Tips: Cookie dough can be balled, frozen on a sheet pan until solid, then transferred to a freezer bag or airtight container. Freeze for 1-2 months. Bake from frozen, adding 1-2 mins to the bake time. Or, thaw frozen dough in the fridge overnight before baking.