Preheat oven to 180°C. Grease a baking dish with EVOO.
Cook pasta as per packet instructions. Drain and pour into the baking dish.
Place the cheeses into the Thermomix bowl. Mill 8 sec/speed 10. Set aside.
Place onion, garlic, 70g of the pepperoni and butter into the Thermomix bowl. Chop 5 sec/speed 7. Cook 5 min/Varoma/speed 1.
Add cornflour, milk, cream, egg and mustard and blend 4 sec/speed 4. Cook 8 min/80°C/speed 4.
Add salt and pepper to taste. Add half of the cheese and mix 4 sec/speed 4.
Pour sauce over the cooked pasta and stir well. Top with marinara sauce and swirl through.
Top with remaining cheese and remaining sliced pepperoni. Bake for 35-40 minutes. Any oil that surfaces as the dish is cooking will be absorbed once it is removed from the oven.
Serve with a garnish of basil and a side salad!