Step 1Heat the oven to 375 degrees. In a 3-quart baking dish, combine the apples, rhubarb, orange juice and zest, brown sugar, cinnamon, cloves, ginger and 2 tablespoons flour. Mix well.
Step 2In a food processor, combine three-fourths cup flour, the pecans and the sugar, and whirl until the nuts are finely ground. Add the butter and whirl until the mixture forms fine crumbs.
Step 3Squeeze the crumbs into lumps and scatter over the apple mixture. Bake until the topping is well browned and juice bubbles at the edges, about 50 minutes.
Step 4While the rhubarb crisp is baking, in a chilled bowl, whip the cream at high speed with powdered sugar and vanilla until it holds soft peaks. Let the crisp cool for a few minutes before serving with the whipped cream.