Prepare Dry Ingredients: Mix flour, salt, and baking soda in a bowl.
Cream Butter and Sugars: In a mixer, add butter, brown sugar, sugar, egg, and vanilla extract. Mix until well combined.
Combine Dry and Wet Ingredients: Gradually add the flour mixture to the wet ingredients, mixing until just combined.
Add Mix-ins: Fold in the salty and sweet mix-ins.
Shape and Chill Dough: Transfer the cookie dough onto plastic wrap, shape it into a log, and chill in the refrigerator for 1 hour.
Slice and Bake: Preheat the oven to 325°F. Cut the chilled dough log into equal slices, place on a baking tray, and bake for 17 minutes.
Serve: Stack the baked cookies and serve with milk.