Rhubarb-Peach Shortcake

To make biscuits: Preheat oven to 425°F. Line a baking sheet with parchment paper or coat with cooking spray. Stir together all-purpose flour, cake flour, baking powder, baking soda and salt in a large bowl. Cut butter and cream cheese into the dry ingredients with a pastry blender or 2 knives until the mixture resembles coarse crumbs. Make a well in the center and add buttermilk; stir with a fork just until a dough forms. Turn the dough out onto a lightly floured surface and knead it very briefly. Pat into a 1/4-inch thickness and cut biscuits with a 3-inch cutter. Reroll any dough scraps and cut them too. Arrange biscuits on the prepared baking sheet, brush tops with egg white and sprinkle with 1 teaspoon sugar. Bake until golden brown, about 10 minutes. Transfer to a rack and let cool slightly. To make filling: Stir together rhubarb, 1/2 cup sugar and lemon juice in a medium saucepan. Bring to a simmer over low heat. Cook, uncovered, for 1 minute. Transfer the rhubarb to a bowl with a slotted spoon. Increase heat to medium and boil the liquid until it is syrupy, about 2 minutes. (You should have about 1/2 cup.) Add the syrup to the reserved rhubarb and set aside. Blanch peaches in boiling water for 1 minute. Remove with a slotted spoon and refresh under cold water. Slip off skins. Cut the peaches in half, remove pits and thinly slice. Add to the rhubarb and stir gently to mix. Whip cream in a chilled bowl until firm peaks form. Fold into yogurt. To assemble shortcakes: Slice the biscuits in half with a serrated knife and place bottoms on dessert plates. Spoon the fruit filling onto and around the biscuits. Spoon a little of the yogurt-cream topping over the fruit. Replace biscuit tops and finish with a dollop of topping.