If using a chocolate bar, chop it into small chunks. Set aside.
Add butter to a pan over medium heat. Stir constantly as it melts. It will foam and start to smell nutty. Continue stirring until it turns golden brown. Immediately transfer to a heat-safe bowl to cool.
Let the browned butter cool for about 10 minutes.
In a mixing bowl, whisk the cooled brown butter with the granulated sugar and brown sugar until smooth. Add the vanilla extract and milk, and mix until fully combined.
Stir in the salt, flour, and baking soda until a dough forms.
Fold in the chopped chocolate or chocolate chips.
: Divide the dough into 5 balls and place them on a parchment-lined baking sheet.
Bake at 325°F or 10–12 minutes, or until the edges are lightly golden.
Halfway through baking, gently tap the pan to help flatten the cookies.
Let the cookies cool on the pan for a few minutes before transferring to a wire rack.