1. Preheat oven to 400ºF. Peel, core and cut pears and apples into chunks. In a large bowl, toss fruit with preserves, brown sugar, lemon juice, 1 tsp. cinnamon and 2 Tbsp. water. Spread mixture in a 13" x 9" baking dish and bake, stirring occasionally, until fruit is soft but still holds its shape, 25 to 30 minutes. Remove from oven and cool to room temperature.
2. Raise oven temperature to 425ºF. In a large bowl, mix flour, 1/4 cup sugar, remaining cinnamon, baking powder, baking soda and salt. Blend in butter until mixture resembles coarse cornmeal. Mix sour cream and buttermilk and add to dry ingredients. Stir until a soft, sticky dough forms. Shape dough into 8 2-inch-thick disks and place 2 inches apart on baking sheets. Sprinkle with sugar.
3. Bake 12 to 15 minutes on two parchment-lined baking sheets, until pale golden. Remove from oven, transfer to cooling rack and cool.
4. In a large bowl, whisk cream until it holds soft peaks; whisk in confectioners' sugar.
5. Split cooled biscuits. Spoon some fruit onto bottom half, top with a large dollop of cream and top half of biscuit. Top biscuits with more whipped cream, if desired.