Make the Lemon Curd

1. In a small pot, whisk together sugar and eggs, then add fresh lemon juice and a pinch of salt. Cook on low to medium-low heat while stirring constantly until thickened.
2. Remove from heat and whisk in butter until smooth. Optionally, stir in lemon zest.
3. Let cool and then chill in the fridge.

Prepare the Cookie Dough

1. Cream butter and sugar together until fluffy.
2. Add egg and vanilla, then mix in lemon zest if using.
3. In a separate bowl, whisk together flour, baking powder, and salt.
4. Gradually add dry ingredients to the butter mixture and mix until dough comes together.
5. Wrap the dough in plastic wrap and chill for at least 1 hour.

Roll and Cut the Cookies

1. Roll the dough between two parchment sheets to about 1/4 inch thickness.
2. Cut out sun shapes. For half of the cookies, cut a center circle for the lemon curd to peek through.
3. Place cutouts on a parchment-lined baking sheet.
4. Chill in the fridge for 10 minutes if the dough warms up.

Bake the Cookies

1. Preheat oven to 350°F (175°C).
2. Bake cookies for 8 to 10 minutes until bottoms are set and lightly golden.
3. Cool on the tray for a couple of minutes before moving them to a cooling rack.

Assemble the Cookies

1. Spread a small spoonful of lemon curd on the flat bottom of solid cookies.
2. Top with cookies that have the center cut out and gently press together.
3. Chill assembled cookies for 15 minutes to help set the curd.

Decorate (Optional)

1. Dust with powdered sugar or drizzle with lemon glaze before serving.