In the bowl of a stand mixer or a large bowl with a hand mixer, cream butter and brown sugar together until light and fluffy.
Mix in vanilla and salt.
Slowly beat in flour, until combined. Stir in milk.
Fold in mini chocolate chips.
Refrigerate cookie dough for at least one hour.
Line a mini muffin tin with mini cupcake liners.
Form 12 small balls with cookie dough (you'll likely have some left over).
Heat dark chocolate in a saucepan set over another saucepan of simmering water (or use a double boiler). Stir until chocolate is melted.
Spoon enough chocolate into the each cupcake liner to cover the bottom of it.
Set cookie dough ball into center of each liner.
Pour chocolate over cookie dough balls to completely cover.
Place in refrigerator until chocolate sets, about 30 minutes.