Preheat oven to 325°F.
Beat 3 egg yolks, well. Beat sugar and baking powder into yolks.
Add vanilla and melted butter; mix thoroughly. Add flour, dates, walnuts and graham cracker crumbs; blend well.
In a separate bowl, beat egg whites until they form stiff peaks; fold gently into date mixture. Spread into a buttered 8-inch square-baking pan.
Bake for 30 minutes or until golden brown. Mixture will be set but not hard.
Serve warm or at room temperature. Cut into squares and serve with whipped cream.