Combine dates and 1 cup boiling water in a small bowl; set aside.
Combine 1/2 cup sugar, 1/2 cup brown sugar, 2 tablespoons butter, and egg in a large mixing bowl; beat at medium speed of an electric mixer until blended.
Combine flour and next 3 ingredients; stir well. Add to sugar mixture, beating well. (Mixture will be crumbly.) Stir in nuts and cooled date mixture.
Spoon batter into a lightly greased 13" x 9" x 2" pan. Combine remaining 1 1/2 cups brown sugar, 1 1/2 cups boiling water, and remaining 1 tablespoon butter, stirring mixture well.
Pour brown sugar mixture evenly over batter. Bake at 375° for 35 to 40 minutes. Serve warm with whipped cream.