1. Preheat oven to 375°.
2. Combine first 3 ingredients in a bowl. Add 1/4 cup granulated sugar, 1/8 teaspoon salt, and 1 1/2 tablespoons flour; toss. Arrange mixture in a 13 x 9-inch glass or ceramic baking dish coated with cooking spray.
3. Weigh or lightly spoon 6.75 ounces flour (about 1 1/2 cups) into dry measuring cups; level with a knife. Combine flour, remaining 1/2 cup granulated sugar, remaining 1/8 teaspoon salt, and baking powder in a food processor; pulse 3 times. Add butter, rind, and cheese; pulse until mixture resembles coarse meal. Add buttermilk; pulse until blended.
4. Drop dough by spoonfuls over plum mixture; sprinkle with turbinado sugar. Bake at 375° for 55 minutes or until golden.