In the bowl of an electric mixer, combine the softened butter, zest, sugar, and salt and beat with the paddle until light and fluffy. Add the egg and beat it in well. In three additions, stir in the flour until blended. Spread the dough out, about an inch thick, on a sheet pan, cover with plastic wrap, and chill until firm. You can refrigerate the dough, wrapped well, for up to a week.

When ready to roll, heat the oven to 350 degrees F and line baking sheets with parchment. Allow the dough to soften slightly. You may find it easier to work with half of the dough, keeping the other half chilled; dough that's too warm won't hold its shape well.

Generously flour your work surface. Roll the dough 1/4 inch thick. Dust off excess flour with a clean, dry pastry brush. Cut out the shapes you want, rerolling the scraps to make more cookies. Arrange the cookies 1 inch apart on the lined baking sheets. Bake until the edges turn golden, 15 to 20 minutes. Let cool on the baking sheet on a rack before transferring or decorating.

For the best results, measure your flour by weight instead of volume. (1 cup of all-purpose flour equals 4-1/2 ounces) If you don't have a scale, be sure to use the proper technique when filling your measuring cups.