Heat up the olive oil in a non-stick pan and fry the garlic for about 1 minute. Add the tomatoes, the sugar and the vinegar, season with salt and pepper and leave the mix on the fire for 20 minutes until the sauce thickens.
In the meantime put the spinach in a large strainer and pour boiling water on it until it softens. Let it cool down for a few minutes, then squeeze the excess water out of it and finely chop it. Mix the spinach with the ricotta cheese in a bowl and season well with salt and pepper.
Heat your oven at 200ºC / 428ºF. Using a piping bag, or a regular sandwich bag with one corner cut off start filling the cannelloni with the spinach and ricotta mix.
When the tomato sauce is ready, pour it in a ovenproof dish and lay the cannelloni on top.
In a clean bowl mix the mascarpone cheese with the milk until you get a light fluffy sauce. Pour this sauce on top of the cannelloni.
Top everything off with slices of mozzarella cheese and bake for about 20 to 25 minutes until you get a golden crust.
Recipe by Simply yum at https://www.simplyum.com/amazing-cannelloni-with-spinach-and-ricotta/