Chocolate-Pistachio Sandwich Cookies

FOR COOKIES: In a large mixing bowl beat the butter or margarine with an electric mixer on medium to high speed for 30 seconds. Add the granulated sugar, brown sugar, cocoa powder, baking powder, and nutmeg; beat till combined. Beat in the egg and vanilla. Beat in as much of the flour as you can with the mixer. Stir in any remaining flour with a wooden spoon. Divide dough in half. Cover and chill for 30 minutes, or till dough can be shaped into rolls. Shape dough into two 8-inch rolls. Roll in ground pistachios, almonds, or pecans to coat. Wrap in waxed paper or plastic wrap. Chill dough for 2 hours, or till firm.

FOR FILLING: In a bowl beat butter or margarine till fluffy. Beat in cocoa powder. Gradually add 1 cup of the powdered sugar, beating well. Slowly beat in the milk and vanilla. Gradually beat in the remaining powdered sugar. Beat in additional milk, if needed, to make a mixture of spreading consistency.

Cut dough into 1/4-inch-thick slices. Place 2 inches apart on ungreased cookie sheets. Bake in a preheated 375 degrees F oven for 8 to 10 minutes, or till edges are firm. Remove cookies and cool on a rack.

Spread 1 to 2 teaspoons of the filling over the bottoms of half the cookies; top with remaining cookies, bottom sides down.