Another one my grandmom used to make and no one has the recipe. After hours of searching the web, I finally found it (I didn't even know the name before!). This version is from Linda Paul, who won a Christmas cookie contest in Minneapolis with them.
Butter and flour bottom and sides of a 9-by 13-inch cake pan.
In a large bowl, using an electric mixer on medium speed, cream together butter and granulated sugar.
Add egg yolks, one at a time, and beat until fluffy.
Add vanilla, lemon rind and lemon juice and beat to combine.
Gradually add in baking powder and flour.
In a medium bowl using electric mixer on high speed (with clean beaters), beat egg whites until stiff.
Fold egg whites into batter.
Gently spread batter into prepared pan.
Evenly sprinkle top with finely chopped walnuts and bake 25 to 30 minutes.
Remove to a wire rack.
Cool until cake shrinks away from sides of pan (about 15 minutes).
With a small round biscuit cutter (or a glass), periodically dipped in powdered sugar, cut one circle (don't remove it), then cut another circle halfway down the first one, making two crescents and one oval scrap.
Remove from pan and repeat (you can eat the oval scraps;).
Cool crescents completely and dust with powdered sugar.
Store in a tightly covered container for up to 2 days.