Rocky Mountain Mud Pie

Preheat oven to 350 °F (175°C). Prepare brownie batter according to package directions, adding oil, eggs and water as directed. Leave batter in the bowl; set aside. Place pie tin with prepared pie crust on a baking sheet. Pour in walnuts to cover bottom. Spoon 2 cups of the brownie batter over the nuts; smooth top so it is level. Bake, on the baking sheet, for 30 minutes. Cool on a wire rack. Slice into wedges to serve, topping each serving with a dollop of whipped cream.