Melt the butter in a large saucepan.
Add the chopped garlic and shallots and saute (without colour) for one minute.
Add the drained mussels (discard any that are already open), half the basil, white wine and freshly milled black pepper.
Bring to the boil over a high heat and then immediately cover and cook for 4 minutes.
Remove mussels from pan with a slotted spoon and strain off the liquid through a fine sieve into a saucepan.
Simmer this liquid for 10 minutes over a low heat.
After 10 minutes add the rest of the basil, chopped and the tomatoes, leave to infuse over a low heat for a further 8 minutes, keep warm.
In the meantime remove mussels from their shells, discard any that haven t opened.
Place each mussel on a piece of the sliced pancetta and roll up. Skewer horizontally onto wooden skewer and repeat until you have 10 mussels on each skewer.
Place the skewered mussels on a baking sheet.
Take the baguettes and cut into 6 x 8cm/3¼in barrels. Carefully remove the centres from each leaving ½cm/¼in perimeter around the sides and base. Place on a baking tray and bake as directed on packet, reducing cooking time by 3 minutes.
Place mussel skewers under a preheated grill and cook for 2 minutes on either side under a medium heat.
Sprinkle with mozzarella and flash under the grill for a further minute or until the cheese begins to melt.
Remove bread from the oven and place in deep serving dishes.
Pour mussel juice into the centre of the up-right barrel of bread and place skewer of mussels across the top. Serve at once.