Remove the wrappers from the Hershey's Kisses and place the candy in a bowl. Set in the freezer while you prepare the dough.
Preheat oven to 350 degrees F.
Place the softened butter and sugar in the bowl of a stand mixer and mix together until creamy.
Add the egg, vanilla and peppermint extract. Mix until well combined.
In a small bowl, add the flour, salt and baking soda. Whisk together. Add the flour mixture to the mixer bowl, alternating with the milk. Mix until fully combined.
Prepare your baking sheet and line it with parchment paper. Scoop dough (see equipment notes for the cookie scoop I recommend)and roll them in your sanding sugar. Place the unbaked cookies 2 inches apart on your baking sheet and bake for 12-14 minutes.
While the cookies are baking, clear a space in your freezer for the cookies to cool.
Once done baking, remove the cookies from the oven and let cool on the sheet for 3 minutes. Take the unwrapped kisses from the freezer and place one in the center of each cookie. Transfer the cookies to a pan or cool baking sheet and place in the freezer to set. This will prevent your kisses from melting. Remove from the freezer after 15 minutes.