Roast partridges for 18 to 20 minutes. Cut into serving pieces. Slice breasts. Combine partridge pieces in a bowl with olive oil and shallots. Marinate in this mixture for at least 12 hours, turning pieces from time to time.
When ready to serve, remove partridges from marinade and arrange them in a serving bowl. Make a well-flavoured vinaigrette with the oil in the dish by adding wine vinegar, finely chopped chervil or parsley, and salt, freshly ground black pepper and dry mustard, to taste. Pour vinaigrette mixture over partridges; add diced apples and celery; toss and serve.