In an ovenproof (preferably cast-iron) skillet, on medium-high heat, add butter to melt and arrange sliced potatoes on a single layer and cook 3 minutes each side. Set aside on paper towel-lined plate to drain.
In the same skillet, cook the chorizo by crumbling it and cooking for about 10 minutes. Add onion and cook for an additional 2 minutes.
In a bowl, whisk eggs with salt and pepper and pour into skillet and lightly combine.
Arrange potatoes on top and season with chili powder. Top with Parmesan cheese.
Cook until sides are just beginning to set, 2 to 3 minutes.
Transfer skillet to oven and broil until just set in the middle and lightly golden and puffed on top, 2 to 4 minutes.
Serve warm or at room temperature. Cut into wedges. Feel free to top frittata with salsa or avocado slices.
Notes
Serve the frittata with salsa and avocado slices, a side of crusty bread with butter, and don’t forget a strong cup of joe.