Prepare the rhubarb puree, and let it cool.

Spray a 9-inch removable-bottom tart or quiche pan, or 9-inch springform pan, with vegetable oil spray.

In a large bowl, combine the flour and sugar. Using a mixer, your hands, a fork or a pastry blender, cut in the butter until the mixture is crumbly and mealy. Set aside 1/2 cup for topping.

To the remaining flour/sugar mixture, add the baking powder, baking soda, cinnamon, orange zest or oil, and salt. Stir in the egg, vanilla extract and buttermilk or sour milk.

Spread two-thirds of the batter over the bottom and up the sides of the prepared pan. Spread the rhubarb on top of the batter, and spoon or dollop the remaining batter over the rhubarb. Sprinkle with the reserved sugar/flour mixture.

Bake the cake in a preheated 350 degree F oven for 40 to 45 minutes, or until the top crust is golden brown around the edges, and slightly brown in the center. Cool thoroughly. Dust with confectioners' sugar just before serving.

Rhubarb Puree:

Microwave Method: Place the rhubarb in a glass dish or

other microwave-safe 2-quart dish. Toss it with the sugar and cornstarch. Cover the dish and microwave on HIGH power for 5 minutes. Stir the fruit, cover it again, and microwave on HIGH power for an additional 5 minutes, or until the fruit is completely softened. Stir till you have a fairly smooth puree.

Stove-Top Method: Place the rhubarb in a 1 1/2-quart, heavy-bottomed saucepan. Toss with sugar and cornstarch. Cook on low heat, covered, for about 5 minutes. Remove the cover, and cook on medium-low heat to cook down the fruit, stirring occasionally, about 10 to 15 minutes, until the fruit is very soft, and the sauce is smooth and thickened.