Preheat your oven to 350°F (177°C) and line two baking sheets with parchment paper.

In a large mixing bowl, combine granulated sugar and lemon zest, blending in softened cream cheese and butter until light and fluffy.

Gradually add egg yolk, fresh lemon juice, salt, and vanilla to the mixture.

Slowly incorporate all-purpose flour until just combined to create a smooth, sticky dough.

Transfer dough into a pastry bag and pipe onto the prepared parchment in 1½ inch circles.

Bake for 10 minutes until edges are lightly golden and centers are soft.

Let cookies cool on the baking sheets before transferring to a wire rack.

Prepare the filling by beating softened butter and sifted powdered sugar until smooth. Mix in lemon zest and juice until creamy.

Spread or pipe filling onto the flat side of one cookie and top with another to form a sandwich.