Preheat oven to 350°; In a bowl, combine the flour, 1 cup brown sugar, baking powder and salt. Melt 1 tablespoon of butter; combine with milk. Stir into flour mixture until smooth. Fold in dates and walnuts. Transfer to a greased 8-in. square baking dish.
In a large saucepan, bring remaining 1 cup brown sugar and water to a boil. Cook and stir until sugar is dissolved. Remove from the heat; stir in remaining 1 tablespoon butter until melted. Pour over batter.
Bake until a toothpick inserted near the center of cake comes out clean, about 50-60 minutes. Serve warm. If desired, top with whipped cream.
