Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a mixing bowl, cream together butter, granulated sugar, and brown sugar until light and fluffy.
Beat in the egg and vanilla extract until fully combined.
In a separate bowl, whisk together flour, baking powder, and salt. Gradually add to the wet ingredients to form a soft dough.
Scoop tablespoon-sized portions of dough onto the baking sheet, spacing them 2 inches apart.
Bake for 10–12 minutes, or until the edges are lightly golden. Let cookies cool completely.
Once cooled, gently spread or pipe vanilla pudding onto the flat side of half the cookies, then sandwich with the remaining cookies.
Heat heavy cream until just steaming, then pour over chocolate chips. Let sit for 2 minutes, then stir until smooth.
Spoon chocolate ganache over the tops of the cookie sandwiches and allow to set before serving.