We prepared three batches of shortbread using a different zest in each, then cut each kind into a different shape.
Using an electric mixer fitted with the paddle attachment, cream butter until light-colored and fluffy. Beat in sugar, zest, and matching extract.
Mix together flour and salt and mix into butter mixture on low speed just until combined. Do not overmix.
Knead a few times on a lightly floured board and roll out to a thickness of 1/4 inch. Cut into desired shapes with well-floured cookie cutters and transfer to a parchment-lined baking sheet. Prick each cookie with a fork a few times and chill until firm, about 30 minutes.
Heat oven to 350 degrees. Bake shortbread for about 20 minutes, or until it just begins to brown. Cool completely on a rack. Shortbread will keep for a few weeks in an airtight container.