Preheat your oven to 375 degrees F. Line a baking sheet with parchment paper or a silicone mat.
In a large mixing bowl, beat together butter and 6 tablespoons sugar until fluffy, about 1 minute. Add apple cider mix and vanilla. Mix until evenly combined, scraping the sides of the bowl as needed.
In a medium mixing bowl, stir together the flour and salt. Add the dry ingredients to the wet ingredients and mix until just combined. (The dough will look dry and like it's not coming together.)
Add milk to the dough and mix until the dough comes together and forms a ball.
Use a small cookie scoop to portion the dough onto the prepared baking sheet, spacing them 1-inch apart. Use your hands to roll the dough into balls. Place 2 tablespoons of sugar in a small bowl, and roll each dough ball in the sugar until coated. Return to the baking sheet. Use the flat bottom of a drinking glass to press down on the cookie dough balls until about 1/4-inch thick.
Bake for 12 to 15 minutes, or until the cookies are set and the bottom edges are just starting to turn golden brown. Remove from the oven and cool on the pan for 3 minutes. Transfer to a wire cooling rack to cool completely.