Preheat the oven to 350 degrees F. Butter a 3-quart baking dish. Melt 6 tablespoons butter in a large skillet over medium heat. Add the onion and 1/4 teaspoon sugar and cook until soft and golden brown, 8 to 10 minutes. Transfer to a large bowl, reserving the skillet.
Meanwhile, bring a large pot of salted water to a boil; add the noodles and cook until al dente, about 6 minutes. Drain the noodles and add to the bowl with the onion mixture; season with salt and pepper.
Pulse the eggs, cottage cheese, sour cream, milk, cinnamon, orange zest, the remaining 1 tablespoon sugar and 1 teaspoon salt in a food processor until smooth. Add to the noodles and toss, then transfer the mixture to the prepared dish. Melt the remaining 2 tablespoons butter in the skillet over medium heat, add the cornflakes and toss. Sprinkle over the pasta and bake until just set, 35 to 40 minutes. Let rest 10 minutes before serving.