Prepare macaroni as usual by tossing in boiling salted water and draining when al dente, then stirring in a tablespoon of olive oil to keep the noodles from sticking. Brush the bottom of an oven dish with olive oil, squeeze in some garlic and spread over the surface. Pour in macaroni, into which you have stirred in grated truffle, and top with grated cheese. Pour heavy cream over the ensemble and finish off with salt, pepper and freshly grated nutmeg. Pop the dish in the oven until bubbling and golden. Top with truffle slivers and serve piping hot.