How to Make It
Preheat oven to 400°.
To prepare filling, combine first 6 ingredients in a large bowl; toss gently to combine. Spoon mixture into a 9-inch square glass or ceramic baking dish coated with cooking spray.
To prepare biscuits, weigh or lightly spoon flours and cornstarch into dry measuring cups; level with a knife. Combine flours, cornstarch, 2 tablespoons granulated sugar, and next 3 ingredients (through salt) in a medium bowl, stirring with a whisk; cut in 1/3 cup buttery spread with a pastry blender or 2 knives until mixture resembles coarse meal. Make a well in center of flour mixture; add rice milk and egg, stirring just until moist.
Turn dough out onto a heavily floured surface; knead lightly 5 to 6 times. Roll dough into a 12 x 12-inch square. Brush 1 tablespoon melted buttery spread over dough; sprinkle evenly with brown sugar. Roll up dough tightly, jelly-roll fashion. Pinch seams and ends to seal. Cut into 12 (1-inch) slices; place in a single layer on top of filling. Bake at 400° for 40 minutes or until biscuits are golden brown.