1. Remove the nerves and cut the kidneys into approximately 2 cm cubes (if it has not already been done by the butcher). If you prefer a mild taste, blanch them for 1 minute.
2. Peel and slice the shallots.
3. Melt the margarine in a pan or sauté pan. Add the kidney cubes and shallots, and cook for about 3 minutes without burning them.
4. Pour a tablespoon of whisky (or cognac) over the mixture and flambé.
5. After the flames have died down, reduce the heat, add the mustard, and let the mixture cook for 2-3 minutes while stirring to prevent burning the mustard.
To finish, add the fresh cream, moderately salt and pepper, stir, bring to a boil one last time, and serve immediately.