In mixer with paddle attachment, add 1/2 c butter, 3/4 c sugar and beat. Add an egg and 1.5 t vanilla extract,. Mix in 1 3/4 c flour, 1/2 t baking powder and 1/4 t salt.
Scoop batter into baking pan, and press flat with your fingers. Bake at 350 for 20 minutes, or until a toothpick inserted comes out mostly clean. Let cool completely.
Beat 4 TB butter and 3 oz cream cheese until fluffy. Add 3/4 t vanilla and mix. Add 2 c powdered sugar
Spread the frosting over the cooled cookie, decorate with candy, and then slice to serve.