Preheat the oven to 350 degrees F (175 degrees C). Grease two 12-cup muffin tins or line cups with paper liners.
Stir flour, cocoa powder, baking powder, and salt together in a bowl. Cream butter and sugar together in a separate bowl using an electric mixer until light and fluffy. Add eggs 1 at a time, beating well after each addition. Mix in vanilla extract. Pour in flour mixture and blend well. Beat in milk, Irish cream liqueur, and coffee until evenly blended. Fold in chocolate chips.
Spoon batter into the prepared muffin cups, filling each 2/3 full.
Bake in the preheated oven until tops spring back when lightly pressed, 15 to 18 minutes. Cool in the tins for 5 minutes. Transfer to a wire rack to cool completely.
