Place the chocolate and butter in a microwave-safe bowl. Heat at half power in 30-second increments until the butter has melted and the chocolate melts when stirred. Stir until smooth. Set aside to cool.
Preheat oven to 350°F (175°C). Grease 48 mini muffin cups or line them with paper liners.
Add the eggs, sugar, and Irish cream to the cooled chocolate mixture. Use an electric mixer (or mix by hand) to mix until thoroughly combined.
Stir in the flour and salt, mixing just until combined. Stir in the chocolate chips.
Divide the batter among the muffin cups, filling each almost full. (I use a#40 scoop.)
Bake 10 to 15 minutes, or until a pick inserted into the center comes out with moist crumbs. Cool in the pan on a wire rack.
Notes
Store in an airtight container at room temperature up to 3 days or freeze up to 2 months.