Soak lemon grass in water for 2 minutes. Chop very fine. Slice beef into 1/2 inch thick slices. In food processor, process into a paste, garlic, sugar and shallots. Then add fish sauce, sesame seeds, pepper, sesame oil and lemon grass. Allow to marinate in refrigerator overnight. Preheat oven to 450 degrees. Cover the bottom and sides of a baking pan with aluminum foil. Spread the beef slices over the bottom of the pan allowing the pieces to touch and overlap. This will prevent the meat from drying out. Bake for 10 minutes. Cut each rice paper in half, put a slice of beef on one end, with a sprinkle of mint leaves and cilantro. Roll cylinder fashion and serve.