Preheat the oven to 400 degrees.

In a medium bowl cream the butter and powdered sugar. Stir in the lemon juice and the lemon zest.

In a small bowl combine the flour and salt. Add the flour mixture to the butter mixture and stir until a dough forms. Stir in the vanilla.

Roll the dough into 1 inch balls and place on a cookie sheet.

Gently push down on the cookie with the bottom of a glass. Then dip the glass in sugar and place it back on the cookie to flatten it. Repeat with remaining cookies.

Bake for 8-9 minutes or until the edges begin to brown.

Remove from oven, allow to cool for 2 minutes, then move to a wire rack to cool completely.

To make the buttercream beat the butter until smooth. Add in the powdered sugar and mix well. Stir in the lemon curd.

Set out 12 of the cookies, flat side up.

Place the filling in a zip top baggie. Snip off the end and pipe the filling onto each of the 12 cookies. Place another cookie, flat side down, on top of the filling to make a sandwich cookie.