Sauce: Add a drizzle of oil to a 12" cast iron skillet (or regular pan) and fry the onion until soft & golden. Add garlic and fry for 1-2mins longer, then pour in passata and stock. Add parsley, chilli flakes, sugar, salt & pepper and bring to a gentle simmer. Stir occasionally over low-medium for 30mins to marry the flavours and thicken the sauce. Meanwhile...
Pesto: Add basil, pine nuts, parmesan, garlic, extra virgin olive oil, salt and pepper to a food processor and blitz until well combined (use a spatula to scrape down the sides in between pulses if needed).
Filling: In a medium-sized mixing bowl combine the pesto with ricotta and half the mozzarella. Test for seasoning then mix in the egg until evenly combined.
Cannelloni: Place a piping bag over a pint glass and add the pesto ricotta. Snip off the bottom to around half the diameter of the cannelloni. One by squeeze the pesto ricotta into the cannelloni until they're all packed full.
Prep to Bake: Scoop out around half of the cooked sauce and place into a jug or bowl to one side. Tightly place the filled cannelloni on to the sauce, then pour over the rest, making sure all the cannelloni is covered. If you were using a regular pan just pour half of the sauce into a baking dish, then top with cannelloni and the rest of the sauce.
Bake: Cover with foil and bake in the oven at 180C/350F for 30mins. Then remove the foil, top with the rest of the mozzarella and parmesan, then place back in the oven at 200C/400F for 10-15mins, or until golden/crisp on top.
Serve: Sprinkle over any leftover basil/parsley you've got, then serve up and enjoy!