Cotechino is a monster of a sausage made from pork, pork rinds and spices. The fresh version is hard to get hold of, but you have a fighting chance around this time of year - it's a traditional meal in Italy in New Year's Eve.
I got mine from Gastronomica at Borough Market last year. However, if you can't find any fresh, most good Italian delis will have pre-cooked cotechino in foil packets. If that's what you're using, follow the instructions on the packet for cooking times.
Mostarda di Cremona is made of fruits preserved in a spicy, mustardy syrup. In the jar it looks exactly like glacé fruit, which I suppose it is. But the taste is unique. I love it with charcuterie and cheese. Otherwise use another spicy fruit relish. I bow to no man in my affection for Branston pickle, but that is definitely not what's called for here.
If you have one, you can use your favourite recipe for boiled lentils to go with the sausage - and I've also included a recipe for a more 'sophisticated' lentil dish that I often make.