In a large mixing bowl, beat the unsalted butter, granulated sugar, and light brown sugar together until the mixture is light and fluffy, about 2-3 minutes.
Mix in the salt, milk, and vanilla extract until well combined.
Gradually sift in the all-purpose flour and unsweetened cocoa powder, mixing until just combined, then fold in the miniature chocolate chips.
Cover the bowl with plastic wrap and refrigerate the dough for at least 30 minutes.
Once chilled, scoop out small portions and roll them into balls, about 1 inch in diameter, placing them on a parchment-lined baking sheet.
In a double boiler or microwave, melt the melting chocolate until smooth, stirring to avoid burning.
Dip each cookie dough ball into the melted chocolate, ensuring it’s fully coated, and place back on the parchment paper.
While the chocolate is still wet, sprinkle with sprinkles or additional chocolate chips, then let sit at room temperature or refrigerate until the chocolate has set.
