Make-Ahead Spanish Frittata

["Preheat oven to 400u00b0F. Toss potatoes, shallots, paprika, 1/4 cup oil, and 1 1/2 tsp. salt on a 13x9"" rimmed baking sheet or metal baking dish. Bake, tossing halfway through, until potatoes are fork-tender and golden brown, 30-35 minutes. Let cool slightly. Reduce oven temperature to 325u00b0F.", "Whisk eggs, sour cream, mustard, and remaining 1 1/4 tsp. salt in a large bowl. Stir in potato mixture. Line the same sheet you used to roast the potatoes with parchment (don't worry about washing pan), leaving some overhang on two sides. Grease parchment generously with oil, then pour egg mixture into pan. Bake frittata until center is just set, surface is puffed, and edges are lightly golden brown, 30-35 minutes. Let cool at least 30 minutes.", "Run a knife around the edges of frittata, then use parchment overhang to carefully lift it out of pan and transfer to a cutting board. Let cool to room temperature, then cut into desired shape.", "Frittata can be made 5 days ahead. Chill whole or in pieces in an airtight container."]