Put oven rack in middle position and preheat oven to 325°F. Lightly oil muffin cups.
Blend together all pudding ingredients in a blender until smooth, then divide batter among muffin cups.
Stir together sugar and cornstarch in a 9- to 10-inch glass or ceramic pie plate.
Add rhubarb and toss to coat, then spread in one layer.
Bake puddings and rhubarb, side by side, carefully turning rhubarb over once halfway through cooking, until puddings are just set and edges are pale golden, 35 to 45 minutes.
Remove puddings and rhubarb from oven at the same time. Set rhubarb aside and cool puddings in muffin pan on a rack 5 minutes (puddings will sink slightly).
Run a thin knife around edge of each pudding, then invert a platter over pan and invert puddings onto platter.
Transfer puddings, right side up, to plates and serve topped with rhubarb and its juices.
