1. Preheat the oven to 350°. Generously butter a 9x13-inch baking dish. Arrange the rhubarb in the dish in a single layer. Pout on the orange juice and sprinkle with 1 cup of the sugar. Bake, uncovered, for 30 minutes and then set aside.
2. Generously butter a 9x5-inch loaf pan or narrow rectangular baking dish. Sprinkle 1/2 cup of the sugar over the bottom. Arrange the baked rhubarb in rows over the sugar, curved side down. Coarsely chop any that is left and distribute it over the 1-inch lengths.
3. Transfer the liquid from the baked rhubarb to a small saucepan. Place over medium heat and reduce to 1/2 cup. Set aside.
4. Combine the flour, the remaining 1/4 cup sugar, the baking powder, and salt. Whisk to blend thoroughly. Cut in the butter until the mixture is crumbly. Whisk the eggs and milk together and stir in the orange zest. Add to the flour mixture. Toss to form a soft dough. Spoon over the rhubarb and smooth the surface. Bake for 30 to 40 minutes or until a wooden pick inserted into the center comes out clean. Cool on a rack for 10 minutes, then invert onto a serving plate. Spoon the reduced liquid over the warm cake. Serve warm, sliced into 1-inch-wide pieces, the width of the rhubarb rows.