Remove the sausage meat from the casing and place the meat in a bowl. Mix in the mascarpone, Parmesan, pesto, egg, salt and white pepper. Preheat the oven to 350 degrees F. Spoon and spread 1/3 of the pasta sauce into the bottom of a 9" x 13" baking pan. Cut each lasagna sheet in half width wise. Set one of the half sheets on a work surface. Place 3 to 4 Tbsp. of the sausage mixture in a row at the end of the sheet. Roll the pasta into a cylinder and set in the baking dish. Repeat with the remaining pasta sheets and filling. Top the cannelloni with the remaining pasta sauce; sprinkle with the mozzarella cheese. Cover and bake for 25 minutes. Uncover and bake for 10 minutes more, or until the mozzarella cheese is light golden.
Note: For other ways to use mascarpone cheese, see the recipe options below.