Preheat the oven to 350°F (180°C).
In a large bowl, cream together the butter and sugar until light and fluffy. Mix in the vanilla extract and egg.
In another bowl, whisk together the flour, baking powder, and salt. Gradually add to the butter mixture, mixing until just combined.
Scoop tablespoons of dough onto a baking sheet lined with parchment paper, spacing them 2 inches apart.
Bake for 8-10 minutes, or until the edges are lightly golden. Allow cookies to cool completely on a wire rack.
Once cooled, spread half of the cookies with vanilla frosting, then top with another cookie to create a sandwich. Ad sprinkles if desired.