preheat oven to 400˚

mix rhubarb with sugar and just enough water to keep it from scorching, bring to a boil over medium high heat, reduce heat and cook 4-5 minutes until the rhubarb is just about cooked

mix the corn starch with a 1/4 cup of water, add some of the hot juice to the cornstarch, and pour all of it in the rhubarb mix

cook and stir until bubbly, cook 1-2 minutes then remove it from the heat

mix the flour, 1/3 cup of sugar, and baking powder together, cut in the butter until it resembles crumbs

mix the egg and the buttermilk together and then lightly mix it with the flour and butter mix

stir only until it comes together

pour the warm fruit in a 1 1/2 quart baking dish, drop the biscuit dough on in six plops, sprinkle the biscuits with the remaining sugar

bake 20-25 minutes until the biscuits are cooked through and the fruit is bubbling