Preheat the oven to 350 degrees F and line a baking sheet with parchment paper.

In a mixing bowl, cream the 1/2 cup softened butter with the granulated sugar until light. Add the egg yolk and 1 teaspoon vanilla extract, then mix until combined.

Stir in the flour, baking powder, and salt until a soft dough forms. Roll the dough to 1/4-inch thickness and cut into 8 small rounds.

Place the rounds on the baking sheet and bake for 10 to 12 minutes until the edges are lightly golden. Cool completely on a wire rack.

For the filling, beat the remaining 1/2 cup softened butter with the powdered sugar and heavy cream until smooth. Mix in the second teaspoon of vanilla extract.

Stir the melted candy corn into the buttercream to create a gentle swirl.

Spread or pipe the filling onto the flat side of four cooled cookies. Top each with a second cookie and press gently to seal.