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1
Preheat the oven to 400F, with racks in the center and lower third.
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2
Line a rimmed baking sheet with parchment paper; set aside.
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3
In a large bowl, toss together the raspberries, rhubarb, 1 1/4 cups sugar, tapioca, lemon juice, and pinch of salt; stir to combine.
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4
Let stand 15 minutes, stirring once or twice.
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5
Divide the filling among six to eight 10-ounce baking dishes, or pour into a 2 1/2-quart baking dish.
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6
In a medium bowl, whisk together both flours, remaining 1/4 cup sugar, baking powder, baking soda, lemon zest, and remaining 1/2 teaspoon salt.
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7
Using a pastry blender, cut in butter until the mixture resembles coarse crumbs.
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8
Add the yogurt, and stir with a fork to form a moist dough with the consistency of thick cake batter.
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9
Using a large spoon, top filling with dollops of dough, leaving a 1-inch border.
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10
Brush dough with cream.
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11
Transfer baking dishes to prepared baking sheet; bake, rotating sheet halfway through, until biscuits are golden brown and juices are bubbling, 50 to 60 minutes.
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12
(If the biscuits are browning too quickly, cover loosely with aluminum foil during the last 15 minutes of baking.)
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13
Cool on a wire rack, at least 1 hour.
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14
Serve warm or at room temperature.
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15
This easy, biscuit-style topping is dropped by heaping tablespoons onto the fruit filling before baking.
