Preheat oven to 350. In a mixer, blend butter and sugar until combined. Add in lemon zest, lemon juice and egg and mix until fluffy. Dump in flour, baking soda and salt and combine.
Prepare cookie sheet with silpat or parchment paper. On a small plate, roll teaspoons of dough into balls and then roll in the remaining sugar. Add to cookie sheet. Bake for about 12-14 minutes or until the edges are lightly golden. Remove from sheet and cool on racks.