Rinse the split peas in a sieve under the running tap. You do not need to let them soak in water. Bring water to the boil with the peas, gammon and bacon. Let it boil and skim off the floating scum. Pour off, rinse again and put peas and meat back on the fire with clean water.

While peas and meat are gently cooking you prepare the vegetables: Cut the skin of the celeriac, peel the potatoes, and dice celeriac and potatoes. Peel the carrot and dice it. Cut the leeks and wash them. Add the vegetables to the pan and let simmer until the peas are done (one and a half to two hours, the split peas must be broken).

Take the meat out of the pan, remove rind and bones, and cut it in small pieces. Return the meat to the pan. Wash the sprigs of celery, and chop or cut the leaves. Twenty minutes before the end of cooking add the whole smoked sausage and the celery. Taste, finish off with pepper and salt.

The pea soup is still fairly liquid. Let it cool completely and reheat it the next day, or freeze in portions. When you want to freeze the soup, add the smoked sausage when reheating, or divide the sausage in equal quantities over the portions.

Take care when you reheat the soup to do this very gently. To serve: In large bowls, with bread. Older cookbooks (nineteeth century) prescribe toasted white bread, later cookbooks rye bread (pumpernickel), with "katenspek" or other cooked and smoked streaky bacon. And no one will punish you if you use French bread instead.