Preheat oven to 350℉ and line cookie sheets with parchment paper or silicone mat.
In the bowl of a stand mixer, cream brown sugar with peanut butter and butter until smooth and creamy, about 3-4 minutes.
Add egg, milk, and vanilla, continuing to mix until blended and smooth.
Add flour, baking soda, and sea salt to the mixture and stir to combine.
Fold in chocolate chips.
Drop dough, using about 1½-2 tablespoons of dough onto prepared pans, spacing about 2 inches apart.
Lightly press down on cookie dough with a fork making cross hatches on the tops of cookies. Cookies should be about a ¼ inch thick.
Bake in preheated oven for 6-8 minutes. Cookies should just be turning golden.
Allow to cool on the pan for 2 minutes before transferring the cookies to a wire rack to cool.