Preheat oven to 350 °F.
Use an electric mixer to beat together the powdered sugar and margarine; add vanilla and lemon zest.
In a small bowl, combine the matzah cake meal, potato starch, and salt.
Add dry ingredients to wet , and mix until the dough forms a ball. The dough will be very soft, but holds up well to being handled.
Roll tablespoons of dough into balls and place on cookie sheets lined with either parchment or a silicone baking sheet.
Use your finger or thumb to gently make an indentation in the middle of each ball. The cookie may crack a little around the edges.
Fill each indentation with about 1/4 teaspoon of your favorite fruit preserves.
Bake about 14 minutes or until barely golden.
Cool on the cookie sheet for a couple minutes, then transfer to wire rack to cool completely.
The cookies are a little crumbly, so handle with care!
This recipe is adapted from Food Allery Momma’s dairy, egg, and nut free thumbprint cookies.