Preheat oven to 400°F.
Pierce sweet potatoes with a fork. Place sweet potatoes on a foil-lined baking sheet. Roast 30 minutes, or until tender. Let stand until cool enough to handle.
While sweet potatoes roast, bring milk to a boil. Combine egg yolks, whole eggs, salt and pepper in a large bowl, stirring with a whisk. Add half of hot milk to egg mixture, stirring constantly with a whisk. Whisk in remaining hot milk into egg mixture.
Cut roasted sweet potatoes in half, and scoop flesh into a food processor or blender. Add 1/2 cup milk mixture, and process until pureed. Whisk pureed sweet potato mixture into milk mixture in bowl. Stir in cubed bread. Set aside, stirring occasionally.
Heat a large saute pan over medium-high heat, and add oil. Add onion and another pinch of salt, and saute 5 minutes, or until tender. Stir in kale and water. Cover and cook 3 minutes, or until kale is tender. Stir kale mixture into bread mixture. Stir in 1/2 cup cheese. Spoon into a buttered 2-quart baking dish, or divide evenly among 16 muffin cups (1/2 cup) coated with cooking spray. Sprinkle evenly with remaining 1/4 cup cheese. Bake for 30-35 minutes, or until pudding is puffy, set, and lightly browned. Serve warm.