For the sauce, heat half the oil in a pan
and sizzle the pancetta for 5 mins, until
just starting to crisp. Then add the onion,
garlic, thyme, bay and sugar, and cook
until the onions are golden. Splash in the
vinegar, sizzle for a moment then tip in
the tomatoes. Swoosh the wine around
the tomato tins to wash out every last
bit and tip into the sauce. Season with
chilli and a pinch of salt and simmer
for 30 mins until rich and thick.
Meanwhile, heat the oven to
200C/180C fan/gas 6. Scoop out the
middle of the marrow, leaving a little
in the bottom to form a base. Drizzle a baking dish with a
little oil, arrange the marrow in the
dish and roast for 30 mins.
Spoon the sauce into the middle of
each marrow slice, cover with foil and
bake for 30 mins. Remove the foil, scatter
over the mozzarella and return to the
oven for 10 mins until the cheese has
melted and the marrow is tender.