Preheat the oven to 350 degrees. In a medium bowl, cream together the butter, brown sugar and vanilla then work in the 2 cups flour. Pat into a 9- by 13-inch pan. Bake until just firm, about 10 minutes.
Beat the egg yolks, granulated sugar, the remaining 6 tablespoons flour, salt and cream and stir in the rhubarb. Pour over the crust. Bake another 50 minutes.
Beat the egg whites until soft peaks form, then slowly add the 3/4 cup sugar until the egg whites form stiff peaks. Spread this over the top of the custard and bake until brown, about 15 minutes. Allow to cool a little before cutting.
Nutrition information per bar:
Calories350Fat15 gSodium150 mg
Carbohydrates51 gSaturated fat9 gCalcium88 mg