Preheat the oven to 350 degrees F. You will need a 9-inch square baking dish.
Fruit Filling: Stir the brown sugar and Clabber Girl Cornstarch together in a saucepan and add the water, apples and rhubarb. Bring to a low boil over medium heat and cook, stirring constantly, for about 8 minutes until the mixture thickens and becomes translucent.
Remove from the heat, stir in the vanilla and pour into the baking pan. Set aside and allow to cool somewhat.
Drop Biscuit Dough: Whisk together the flour, sugar, Clabber Girl Baking Powder and salt. Using a wooden spoon, stir in the buttermilk till the mixture gathers into a ball. The dough should be blended and quite sticky. Do not knead the dough! Add a few more tablespoons of buttermilk if necessary.
Drop the biscuit dough over the fruit in the prepared pan. Sprinkle brown sugar evenly over the top.
Bake for about 25 to 30 minutes in preheated oven, or until the filling is bubbly and the biscuits are browned. Serve warm.
Recipe submitted by Mani Niall.