The sweet chestnut purée can be bought cheaply in jars or cans, or you can make it yourself. The cans and jars will come in varying sizes, depending on what country they are from.
Recipes to make your own usually call for adding milk, sugar and vanilla to cooked, peeled chestnuts.
Savoury chestnut purée you need to make yourself. You serve it as a side on the dinner plate. There are many recipes, some of which have you simmer raw peeled chestnuts in a stock with some flavouring ingredients such as bay leaves and celery, then remove the chestnuts, and mash with cream and seasoning.
You can also buy chestnut purée unsweetened, which you could then turn into savoury or sweet according to your needs — or just use as is.
Literature & Lore
Fannie Farmer’s recipe for a savoury chestnut purée:
“Remove shells from chestnuts, cook until soft in boiling salted water; drain, mash, moisten with scalded milk, season with salt and pepper, and beat until light.” Farmer, Fannie Merritt. The Boston Cooking School Cookbook. 1918.
New Larousse Gastronomique gives these directions for a savoury purée,
“Purée de marrons. Shell the chestnuts, leaving the inner skin intact. Plunge them into boiling water, drain and skin. Cook in white stock seasoned with a little celery. Drain, and rub through a fine sieve. Warm this purée in a saucepan, stirring constantly. Just before serving, add fresh butter and a few tablespoons fresh cream.” New Larousse Gastronomique. Paris: Librarie Larousse. English edition 1977. Page 218.