BLINTZES: Using a blender, mix the eggs, milk and flour at low speed. Add the Grand Marnier. Once the batter is well mixed and coats the spoon with a thin film, refrigerate, covered for 1 hour in a pitcher or bowl.
Stir the batter thoroughly and before making the crepes, test the liquid by dunking a spoon in the mixture; again, it should coat the spoon with a thin film. Adjust by adding milk if necessary.
Using a 8-10" nonstick pan, spray with oil, and heat the pan over medium-high heat. Pour about one cup of batter to coat one pan. Once covered, pour a thin layer of batter into the heated pan, swirling to coat if necessary.
When the crepes pull away from the edge of the pan in about 20 seconds, remove from the heat, tap them lightly or run a knife across the edge of the pan to release, and invert the crepes on a dry towel to cool. Stir the batter at brief intervals to re-suspend the ingredients.
FILLING: Mix together the ricotta, mascarpone, sugar, vanilla extract, lemon zest and a small pinch of salt.
ASSEMBLY: With the cooked side up, spoon about 1/4 cup filling inside the center of the wrapper.
Fold and hold the two opposite sides of the crepe over the filling until they almost meet and then fold over the ingredients pulling the stuffing toward you.
Fold the crepe over until you form a seam on the blintz. Set finished 2-inch by 1 1/2-inch flat "eggroll" shaped blintz on a dry towel with the seam side down.
COOK: Melt butter or margarine in a skillet over medium high heat, beginning with the seam side down. Saute each blintz until golden brown, carefully so the cheese does not escape.
Flip the blintz onto the other side. Lower the flame and cook slowly, about 2 to 5 minutes to avoid burning the crepe.
TOPPING: Gently toss the rhubarb, strawberries, flour, sugar and lemon and let stand until moist, 5 to 10 minutes.
In a large saucepan, melt the butter and add the fruit mixture. Cook the fruit for approximately 35 minutes, stirring to make sure the fruit does not brown. Cover 5 minutes or until rhubarb is soft.
TO SERVE: Ladle the warm fruit over the blintz and top with a dollop of sour cream. Garnish with a fresh strawberry half.