Mix melted butter and sugar.
Add the egg yolk and vanilla and continue to whisk.
Add the flour and salt and mix together.
Then add the chocolate chips to form a cookie dough.
Scoop dough carefully in a silicone mold.
Place the silicone mold on a baking sheet.
Fill each mold with ¼"-⅓" of cookie dough. Each shot takes about ¼ cup of dough per mold Start with the base and work up the sides. Bake at 350 °for about 20-25 minutes.
Let cool for at least an hour. When the cookies have cooled, freeze for 2-3 hours until cookies are hard. Once the cookies are frozen, remove them carefully from the silicone molds.
In a microwave-safe bowl, microwave the 1 cup of milk chocolate chips at 30-second intervals to melt.Spread the melted chocolate in the cookies with the help of a spoon. (If you do not coat it with chocolate, when you put milk in it, the cookie will become soft.)