In a medium-size bowl, briefly mix the flour and salt. Set aside. In a large bowl with a hand mixer or in the bowl of a standing mixer, blend the butter and confectioner’s sugar well. Add the egg, vanilla extract and lemon zest and juice and mix well. Gradually blend in the flour mixture and stir until a dough forms. Scoop the dough from the bowl and wrap in a zip-top bag or in plastic wrap and refrigerate for 1 to 2 hours.