1. Begin by creaming together the butter, granulated sugar, and brown sugar in a large bowl until smooth and creamy, about 2-3 minutes.
2. Add in the vanilla extract and milk, mixing until fully incorporated.
3. Gradually stir in the flour and salt, mixing until the dough is smooth and no dry spots remain.
4. Fold in the mini chocolate chips, ensuring they’re evenly distributed throughout the dough.
5. Refrigerate the dough for about 20 minutes to make it easier to handle.
6. While the dough chills, melt the semi-sweet chocolate in a microwave-safe bowl in 30-second increments, stirring between each until smooth.
7. Line a muffin tin with paper liners, then spoon a small amount of melted chocolate into each liner, using the back of a spoon to spread it evenly along the bottom and sides.
8. Chill the chocolate-coated liners in the fridge for about 10 minutes until set.
9. Once the chocolate has set, fill each liner with a scoop of cookie dough, pressing gently to flatten.
10. Top the dough with more melted chocolate, ensuring it covers the dough completely.
11. Refrigerate the cups for at least 30 minutes, or until the chocolate has hardened.

From my experience, refrigerating the dough before assembly helps keep the process neat and ensures the cups hold their shape beautifully.