1. Beat together butter and sugar in a large bowl on medium until combined. Beat in zest and juice. Reduce speed to low and add flour and salt, beating until just combined. Chill, wrapped in plastic wrap, at least 1 hour or up to 2 days.
2. Preheat oven to 325 F. and arrange 2 racks in center. Line 2 large cookie sheets with parchment paper; set aside. Roll out dough on a lightly floured surface to 1/4-inch thickness. Using a 2-1/4- inch heart-shaped cookie cutter, cut out shapes and place 1/2 inch apart on prepared cookie sheets. Chill 10 minutes in freezer or 20 minutes in refrigerator.
3. Bake until cookies are set and just golden around edges, 18 to 20 minutes. Cool slightly; using a metal spatula, carefully transfer cookies to racks and cool completely. (Can be made ahead. Store in an airtight container up to 2 days.) Dust with sugar up to 5 hours before serving.