Before you get started, preheat the oven to 400 degrees F
Wash or peel the potatoes then dice them into 1 cm cubes. Add the potatoes to a small pot, cover with cold water and 1 teaspoon of salt, and bring to a boil. Cover, reduce the heat to medium-low, and allow the potatoes to cook until fork tender, which should take 12-15 minutes. Drain the potatoes and set them aside.
If you’re using frozen chopped spinach, defrost it and squeeze out as much water as possible. If you’re using fresh spinach, steam it or blanch it until it’s nicely wilted, shock it in ice water, then squeeze out the water, give it a good chop, and set it aside. 140-150 grams of frozen spinach will yield about ¼ cup squeezed, packed spinach.
Crack the eggs into a medium-sized bowl, add the cottage cheese, ½ teaspoon of salt, and the pepper, and mix well with a fork or a whisk. Add the dry, chopped spinach to the bowl and mix to combine.
Start heating up your 10-inch oven-safe skillet over medium heat. Dice the onion and add it to the skillet, along with a splash of water and the remaining ½ teaspoon of salt. Cover the skillet with a lid to allow the onions to soften. Cook for 5 minutes, stirring occasionally. Once the onions are soft, add the garlic powder. You can use oil to cook the onions if you want, but I don’t think it’s necessary.
Allow any remaining water to evaporate, then add the potatoes to the pan and toss with the onions.
Turn off the heat, and gently pour the egg mixture over the potatoes and onions. Move things around so that the potatoes are evenly distributed throughout the frittata.
Place the frittata into the 400 degree oven and cook until it is puffed, lightly golden brown, and set in the middle. This should take 35-40 minutes.
Remove the frittata from the oven, place the skillet onto a cooling rack or hot plate, and allow to cool for at least 10 minutes before you cut into it. This will allow any excess juices to absorb into the egg and potatoes, and you’ll get much cleaner slices. Plus: The resting time will make it release easier from the pan.
Cut the frittata into 4 big wedges and enjoy now, or store for later.