1/2poundYukon Gold potatoesabout 2 medium unpeeled, halved lengthwise *
8large or extra-large eggs
1/4cupplain yogurtsour cream or creme fraiche
1/4cupfreshly grated Parmesan cheesedivided
2tablespoonsextra-virgin olive oil
3cupsspinachkale, or other leafy greens, torn into pieces
4ounceswhole milk ricotta cheesedrained of excess water
Preheat the oven to 350 degrees.
Bring a saucepan of water to a boil and add 2 tablespoons salt. Add the potatoes and cook 15-20 minutes, until just tender when poked with a fork. Drain, and slice into 1/2-inch wide pieces when they're cool enough to handle.
Crack the eggs into a mixing bowl and add the yogurt, 2 tablespoons of the Parmesan cheese and 1 teaspoon salt. Whisk together until well blended.
Heat the oil in a 10-inch cast iron or oven-proof nonstick skillet over medium heat. Add the onion and cook until soft and translucent, 3-5 minutes. Add the potatoes and spinach. Stir gently to avoid crushing the potatoes, and cook until the greens start to wilt, about 2 minutes.
Pour the egg mixture into the pan. Use a spoon to nudge the egg evenly into the vegetables, then cook until the eggs are set on the bottom, about 3 minutes. Turn off the heat.
Dot the ricotta cheese in blobs evenly over the top of the frittata and sprinkle with the remaining Parmesan. Bake 15-20 minutes, until the eggs are set and no longer runny on top.
Cool 10 minutes before slicing. Frittata can be served warm or at room temperature.
Substitute 2 cups cooked leftover potatoes - cut into 1 1/2" pieces and proceed with step 3.
Leftovers keep up to 3 days in the refrigerator. Reheat slices briefly in a microwave or in a 325 degree oven until warm.
It's possible to freeze frittata for up to a month, wrapped securely. But be aware that the texture can turn soggy after thawing.