Preheat oven to 350 degrees. Mix all filling ingredients and press into a smooth layer in an oiled 13 x 9 inch baking pan. Bake 15 minutes, while you prepare the filling, by boiling the butter, sugar and syrup together for five minutes, then whisking in the cream and vanilla. Stir in the walnuts and pour over the baked crust. Spread evenly, and bake for twenty minutes. Let set, and cut into squares.