Preheat the oven to 180C / Gas 4. Mix together the ricotta, Parmesan cheese and egg in a large bowl. Season with salt and pepper.
Spread 250ml of the pasta sauce over the base of a lightly oiled, large baking dish, measuring about 23x33cm and about 7cm deep.
Arrange three of the lasagne sheets side by side in the dish. Spread with a quarter of the ricotta mixture then top with a third of the mushrooms and a third of the pepperoni sausage. Sprinkle with some of the dried herbs. Repeat layering twice more with the sauce, lasagne, ricotta mixture, mushrooms, pepperoni and herbs. Top with remaining three sheets of lasagne.
Spread the remaining ricotta mixture and sauce over the top, then gently press the lasagne sheets down into the dish, so the sauce comes up around the sides. Cover the dish with foil.
Bake for 35 minutes, then uncover, sprinkle with the mozzarella and continue baking until golden and bubbling, about 20 minutes.
Allow to stand for 10 minutes before cutting into rectangles to serve warm.
Make it lighter
Try using 250g ricotta and 250g fromage frais in place of the 500g ricotta.