Step 1

Heat the olive oil in a large heavy-bottomed pot (an oval Dutch oven or round braiser works well here, but any large pot will do) over medium-high heat. Add the scallion whites, 1 teaspoon salt and a few grinds of black pepper and cook, stirring occasionally, until softened and starting to caramelize, 3 to 4 minutes. Add the oregano, crushed red pepper flakes and garlic and cook, stirring, until the garlic is softened and fragrant, about 1 minute.

Step 2

Add the lemon juice, 5 1/2 cups water, 1 teaspoon salt and a few grinds of black pepper to the pot, scraping up any brown bits that may have formed on the bottom. Put the spaghettoni in the pot and spread it out as much as you can. Bring the water to a boil and cook, stirring frequently to make sure the pasta doesn’t stick to the bottom of the pot, until the pasta is al dente, the mixture looks creamy and starchy and almost all of the water is evaporated, 10 to 12 minutes.

Step 3

Turn off the heat and stir in the Parmesan, ricotta and lemon zest until the cheeses have melted and the sauce is very creamy, about 1 minute. Divide the pasta into 4 bowls and garnish each with scallion greens and a few more cracks of black pepper.