1. Place the pistachios and sugar in a food processor; cover and process until ground. Set aside. In a microwave, melt 1 cup chocolate chips; stir until smooth.
2. In a large bowl, cream butter and brown sugar until light and fluffy. Beat in the eggs, melted chocolate, milk and almond extract. Combine the flour, cocoa, baking powder and salt; gradually add to creamed mixture and mix well. Stir in pistachio mixture.
3. Divide dough into eight portions. Wrap in plastic wrap and refrigerate for 3 hours or until firm.
4. Shape each portion into an 18-in. rope; cut each into six logs. Place 2 in. apart on greased baking sheets. Cut the ends of each log at an angle. Using a small amount of egg white, attach removed pieces to each log, forming branches.
5. Bake at 350° for 10-12 minutes or until set. Remove to wire racks.
6. In a microwave, melt remaining chocolate chips and shortening; stir until smooth. Working in batches, dip cookies in chocolate, allowing excess to drip off. With the tines of a fork, make strokes in the chocolate to resemble bark. Dust with ground pistachios.
7. For mushrooms, pinch half of each marshmallow to form a stem; flatten the other half for cap of mushroom. Dust tops of mushrooms with cocoa. Attach to cookies with a small amount of melted chocolate.
8. Let stand until set. Store in an airtight container. Yield: 4 dozen.