In a large mixing bowl or the bowl of a stand mixer, combine the ½ cup unsalted butter½ cup shortening and 1 ½ cups granulated sugar. Cream until light, then add in 2 large eggs and 2 teaspoons lemon zest.
Sift together the 2 ¾ cups all-purpose flour, 2 teaspoons cream of tartar, 1 teaspoon baking soda and ¼ teaspoon salt. Add to wet ingredients and mix only until just combined.
Combine additional granulated sugar with the remaining 1 teaspoon of lemon zest. Shape dough into 1 ½ inch balls. Roll each ball of dough into the granulated sugar and place on a baking sheet. Bake at 375°F for 10-12 minutes.
Cool on cookie sheet 1-2 minutes before moving to wire rack to cool completely.
Notes
You can substitute the same amount of any citrus zest for the lemon zest
Store cookies in an airtight container for up to 72 hours