Preheat the oven to 180 degrees Celsius/ 360 degrees Fahrenheit (fan oven 160 degrees Celsius/ 320 degrees Fahrenheit) and line a muffin tin with paper liners.
Dry ingredients: Mix flour, baking powder, salt, and chocolate chips.
Cream: In another bowl, beat the egg, sugar, and soft butter until creamy.
Wet ingredients: In a jug, whisk together Bailey's, milk, and vanilla extract.
Combine: Alternating, fold the flour mixture and the liqueur mixture into the creamed egg and butter.
Divide the batter between the prepared muffin cups; they should be about ¾ full.
Bake for 20-25 minutes or until a toothpick inserted in the middle comes out clean.
Let rest in the pan for 5 minutes. Transfer to a wire rack to cool.