In a large mixing bowl, cut together the topping ingredients with 2 knives until they are well combined and crumbly. Be sure the butter is evenly distributed in the mixture. If desired, freeze for up to 3 months, or use immediately.
Preheat the oven to 400 degrees. In another large mixing bowl, combine the sugar and the tapioca and toss until evenly mixed. Add the pears and toss until they are evenly coated with the mixture. Mix in the raisins. Turn the fruit mixture into a 10 x 2 inch deep round baking dish, preferably glass. Sprinkle the crumb mixture evenly over the top and bake the crisp for 15 minutes, then turn the oven down to 375 degrees. Bake for 15 to 20 minutes more, or until the topping is golden. Cool on a rack for 10 minutes, then serve warm accompanied by a dollop of Crema, if desired.
Whisk the cream and the buttermilk together in a bowl. Cover and set in a warm place (a gas oven with just the heat from the pilot light is fine) for 8 hours. Crema may be kept in the refrigerator for as long as a week.
c.1997, M.S. Milliken & S. Feniger, all rights reserved