Add a pinch of salt, stir in the rice and cook until tender. Stir the butter into the rice. Let cool. Add some sugar (if necessary !), mix in the walnuts, stir in the kefir and the whipped cream. SERVING: Rice and pears should be served at room temperature. Arrange on dessert plates. Pour sauce around pears and rice-pudding. Garnish with chopped angelica (or other 'fruits confits').