"Sift together flour and sugar into large bowl; add pistachios.
Blend in 1/2 cup butter with pastry blender to form dough.
Chill for 2 hours.
Roll out on floured pastry cloth to 1/8-inch thickness.
Cut into rounds with floured 2 1/4-inch cutter.
Place oh baking sheet.
Bake at 375 degrees for 7 minutes or until light golden brown.
Melt chocolate over hot water; cool.
Cream 1 tablespoon butter and sugar.
Add egg yolk and chocolate; blend well.
Spread cookies with chocolate frosting; sprinkle with sliv- ered nuts, if desired.