Place the split peas in a large pan. Cover with cold water and bring to the boil over a low heat. As soon as the water boils remove from the heat, cover and leave the peas to soak for 1 hour.

Drain the peas and cover with fresh water. Add the onion stuck with cloves and the bouquet garni. Bring to the boil over a high heat, then reduce the heat and simmer gently for 45 - 60 minutes, or until tender, depending on their age and quality.

Meanwhile, bring another saucepan of salted water to the boil. Add the frozen green peas and simmer gently for 5 minutes, or until very tender. Drain.

Drain the split peas, discarding the onion and cloves and the bouquet garni. Combine the split peas and green peas.

Rub the mixture through a fine sieve with a wooden spoon into the top pan of a double boiler or a bowl which is then placed over a pan of simmering water. Blend the hot milk and 50 g (2 oz) of the butter into the sieved pea mixture and cook over simmering water until the puree is smooth and thick. Season to taste with salt and freshly ground black pepper

Meanwhile, heat the remaining butter and the olive oil in a frying-pan large enough to take the sausages in one layer. Moisten the sausages with warm water and place them side by side in the pan. Fry the sausages for 5 - 6 minutes on each side or until browned and cooked through, turning with a spatula. Remove with a slotted spoon and keep warm.

Pour off the fat. Add the wine to the frying-pan and reduce to half the original quantity over a high heat, stirring with a wooden spoon and scraping the sediment from the bottom of the pan.

To serve, heap the pea puree in a heated serving dish. Arrange the cooked sausages on top and spoon over the wine-flavoured pan juices. Serve immediately.