The Jello gives them a fruity tartness and a fun color. I imagine they were invented in the 50's or 60's back when Jello had it's heyday and everyone was trying to invent a new Jello recipe. My favorite flavor is strawberry, but lime and orange are both good. Just about any Jello flavor will work, although you'll get a better lemon cookie with a standard spritz recipe and lemon extract.
I had forgotten about these for years until last week when Libby requested I make "pink cookies." She had never had pastel cookies before; she just loves pink. Her favorite flavor of ice cream is strawberry only because it's pink. Anyway, I dug through my recipe box and couldn't find the official recipe. I called my mom, but she was no help, having throw the recipe out after giving me her cookie press. In desperation, I turned to my new old copy of James Beard's American Cookery (purchased at a second hand store for all of 50 cents.) I took his recipe for spritz cookies and adapted it. It's a fun cookie that kids love. The bright colors make them perfect for a baby shower or a wedding shower, just change the flavor to match the theme. These are slightly more tough than I like a spritz cookie to be (I blame the gelatin), but the novelty of the Jello makes up for it.
1 c butter
1/3 c white sugar
1 package Jello (not sugar free!)
1 egg or 3 egg yolks
1 t vanilla extract
2 1/2 c flour
1/8 t salt (unless using salted butter. Keep in mind Jello has salt in it)
Cream the butter until very light and fluffy. Cream in the sugar and Jello gradually, and continue beating until very light. Beat in the egg and flavoring. Sift the flour with the salt and add to the mixture. Do not over beat. Press through a cookie press onto cookie sheets. Bake at 400 degrees until the bottom of the cookies turn light tan. The edges will be dry and starting to color as well. Be careful not to over bake. Remove from pan immediately and cool before eating. These cookies are actually best if given a day to rest and mellow before eating. Makes 6-7 dozen depending on cookie shape.