Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Stir in the lasagne sheets and return to the boil. Cook, uncovered, stirring occasionally, until the pasta has cooked through, but is still firm to the bite, about 8 minutes. Drain.
Heat a large frying pan over medium-high heat and cook and stir the sausagemeat, minced beef and garlic until the meat is crumbly, evenly browned and no longer pink. Drain off any excess fat. Stir in the chopped tomatoes, passata, parsley, basil, oregano and sugar. Bring to the boil over high heat, then reduce the heat to medium-low and simmer, stirring occasionally, until the sauce is thickened, about 30 minutes.
Stir together the soured cream, eggs, Parmesan cheese, green olives, salt, black pepper and 1/2 of the mozzarella cheese in a bowl.
Spread a thin layer of the meat sauce evenly over the bottom of a 20x30cm baking tin. Cover with 1/3 of the lasagne sheets, 1/3 of the remaining meat sauce, 1/3 of the soured cream mixture. Repeat this layering 2 more times. Sprinkle the remaining mozzarella cheese evenly over the lasagne.
Bake in the preheated oven until the sauce is bubbly and the top is golden brown, about 30 minutes.
Pre-boiling lasagne sheets
Can be omitted if using ready-to-bake lasagne sheets.