Preheat the oven to 350 degrees. Line cookie sheets with parchment paper or foil.
Using an electric mixer, cream the butter and sugar at low speed until smooth.
Beat in the vanilla and the lemon juice.
At low speed gradually add the flour.
Mix in the walnuts/pecans with a spatula.
With floured hands, take out about 1 tablespoon of dough and shape into a crescent or ball. Continue to dust hands with flour as you make more cookies. Place onto prepared cookie sheets. (Make sure the kids don't play too much with the balls as the butter can melt. Tell them to roll the balls counting to three and then drop.)
Bake for 15-20 minutes until pale golden. Let cool on baking sheets for a few minutes.
When cool enough to handle but still warm, roll in additional confectioners' sugar mixed with the lemon zest. Cool on wire racks.