In a bowl, mix together the flour, baking powder, and salt. In another bowl, beat the butter and sugar until light and fluffy, then add the egg and vanilla. Gradually mix in the dry ingredients until a soft dough forms.
Grease a muffin tin or place cupcake liners, and press portions of the dough into each cup, pressing it slightly up the sides to form a little shell shape.
Bake at 350F for 8-10 minutes, or until the cookie cups are just set and lightly golden around the edges. As soon as they come out of the oven, use the back of a spoon or a small tart shaper to gently press the centers down if needed. This creates space for the filling. Let the cookie cups cool in the pan briefly, then transfer them to a rack to cool fully.
Beat the cream cheese, powdered sugar, and a little whipped topping or cream until smooth and fluffy.