Butter six 5 t0 6-inch gratin or fruit dishes about 1 inch deep and dust with sugar. Arrange on rimmed baking sheet. Toss rhubarb with 1/4 cup sugar, and divide among dishes. Cover each first with parchment and then with foil, and bake until fhubarb is just beginning to release liquid and soften, about 30 minutes.
Puree milk, cream, flour, eggs and yolk, remaining 1/2 cup sugar, and 1/2 teaspoon salt in a blender until smooth. Divide mixture evenly among dishes. Bake, uncovered, until just set, 22 to 25 minutes. Let cool for 20 minutes. Serves 6 (Martha Stewart Magazine)