In a pot sauté the onions in butter till soft. Add the peas and simmer for 15 minutes, then blend and puree to a thickish consistency. Add the stock from the ham hock to give it a slight smokiness.
In a separate pan, sauté the onions in olive oil and garlic for 5 minutes on a low heat. Add the mushrooms and thyme. Tear chunks off the pre-cooked ham hock and mix well. Season if necessary. Wrap the mixture in cling film and roll into a cylindrical shape. Set for 1 hour and slice through the plastic, taking care to take the plastic off afterwards. Place in the soup.
In a mixing bowl, add the salad ingredients, season and serve on the ham terrine. Garnish with the pea shoots and finish with truffle oil.