Cream butter with cream cheese and sugar until blended. Beat in egg yolk and then flour, lemon peel and juice and pistachios until mixed to a dough. If dough gets too stiff for mixer, work in the last of the flour by kneading on board. Shape (see below); bake on cookie sheets at 350° F.
 

Jamprints: Shape scant-tablespoon portions of dough into balls. Roll half the balls in additional finely chopped pistachios and leave other half plain. Bake about 14 minutes. After baking, flatten warm cookies by pressing a thumbprint or back of a teaspoon into center of each. Cool. Dust plain ones with sifted powdered sugar. Fill with jams or lemon curd.