Follow instructions on packaging on how to boil pasta. Make sure pasta is boiled with salt.

Cleaned the mushrooms, chopped and set aside. In a skillet over medium heat, melt butter, add garlic, mushrooms, parsley, thyme, black pepper and salt. Let mushrooms cook in their own juice for about 3 - 4 minutes while stirring occasionally. Add lemon juice and continue to cook for 1 minute. Turn off heat and let cool.

Preheat oven at 180ºC / 350ºF / Gas Mark 4. Combine ricotta, egg, nutmeg, and mozzarella cheese in a bowl and stir until mixed. Add mushroom mixture and stir to combine. Fill up all the shells with the filling. Spread 1.5 cup of tomato sauce in the bottom of a 23cm x 33cm (9" x 13") casserole dish. Place stuffed shells in dish. Spoon remaining sauce over shells and sprinkle with cheese. Bake for 35 min or until sauce is bubbling and cheese is melted.