Preheat oven to 350 degrees F. Spray 8-inch pan with non-stick spray and set aside. In a small bowl, whisk together flour, baking powder, baking soda and salt. In a large bowl, cream together butter and sugar until light and fluffy. Beat in egg, followed by vanilla extract. Mix in half of the flour mixture, followed by the Irish cream and milk, then the remaining flour mixture and mix til well blended. Pour batter into prepared pan.