Preheat oven to 375°. In a large bowl, cream butter and brown sugar until light and fluffy. Beat in milk. Gradually beat cracker crumbs into creamed mixture. Stir in walnuts and 2 cups chocolate chips., Fill 2-in. foil baking cup liners three-fourths full. Place 1 in. apart in 15x10x1-in. baking pans. Bake 10-12 minutes or until set. Remove from pans to wire racks to cool completely., Drizzle with melted chocolate; let stand until set. Store in an airtight container in the refrigerator.