"These cookies are crisp and flaky, and they don't taste lemony. The low sugar content is important because the icing is so sweet. They have a delicate black raspberry liqueur scent once iced, and are beautiful as well, with a shiny glossy finish. You will need a heart-shaped cookie cutter. If you like, sprinkle the frosting with rainbow non-pareils, silver balls, or red sugar. Frosting dries to a high sheen within a half hour or so."
In a medium bowl, beat together the butter, shortening, and 1 cup sugar until smooth and creamy; then add eggs, vanilla, and lemon extract. In a large bowl, mix together flour, salt, and baking powder. Make a well in the middle, and pour creamy mixture into it, folding the dry into the wet until mixed. Stir in 2 tablespoons milk at the end. To make rolling easier, you may cover and refrigerate anywhere from 1 hour up to a few days.
Preheat oven to 350 degrees F (175 degrees C). On a lightly floured surface, roll out dough to 1/8 inch thickness. Use a heart-shaped cookie cutter to cut shapes out of dough. Place cookies 2 inches apart on a baking sheet.
Bake in preheated oven for 6 to 10 minutes. Slightly browned is OK, but not necessary. Remove from baking sheets to wire racks to cool.
Meanwhile, in a medium bowl, beat egg white with an electric mixer until frothy but not stiff. Gradually beat in 1 1/2 cups sugar, then 1/8 cup milk. Mix in raspberry liqueur and cherry-flavored gelatin. Gradually beat in remaining 1 1/2 cups sugar and pinch of salt, mixing until the icing looks about like marshmallow fluff, not quite stiff enough to stand in peaks. Spread icing on top of cookies.