Potato and Kale Frittata

Preheat broiler.

Heat oil in a heavy ovenproof 10-inch skillet (preferably cast-iron; not non-stick) over moderately high heat until shimmering and stir in potatoes with ½ teaspoon salt. Reduce heat to moderately low and cook, covered, stirring and turning occasionally, until tender, about 10 minutes. Transfer potatoes with a slotted spoon to a bowl.

Add onion with a ¼ teaspoon salt to skillet and cook, covered, over moderate heat, stirring occasionally, until softened, about 5 minutes. Add garlic and cook, stirring, 1 minute.

Add ½ cup water, then add kale by handfuls, cooking each handful, covered, until slightly wilted, about 1 minute, before adding next. When all kale is added, continue to cook, covered, until tender, about 5 minutes. (Check occasionally to make sure water has not completely evaporated and add just enough additional, if necessary, to keep kale from burning.)

Stir in potatoes and season mixture with salt and pepper.

Whisk eggs well with milk, ¼ teaspoon salt and ¼ teaspoon pepper and pour over vegetables. Cook, lifting up cooked egg around edge to let uncooked egg flow underneath, for 2 minutes. Reduce heat to low and cook, covered, until set 1-inch from edge (center will still be loose), 4 to 5 minutes.

Remove lid. Sprinkle cheese evenly over frittata and broil, 5 to 6 inches from heat, until center of frittata is set, 2 to 4 minutes.