• In a food processor, pulse flour, confectioners' sugar, salt and lemon zest until combined. Add butter and process until sandy. Add egg yolks and lemon juice; pulse until dough comes together. Divide dough in half and form each into a 1 ½ inch-wide log. Wrap in plastic and freeze until firm, about 2 hours (or up to 1 month).
• Preheat oven to 350°F. Spread granulated sugar on a piece of parchment paper and roll logs over sugar to coat. Slice logs into ¼ inch thick slices and arrange 1 inch apart of a parchment lined cookie sheet. Bake until cookies are golden brown around the edges, about 12 minutes, rotating the sheet halfway through cooking time. Cool cookies on a wire rack. Store in airtight container at room temperature up to 5 days.

For the Frosting:

• In a small bowl mix all frosting ingredients until fluffy. Frost cooled cookies.