Bring the milk to a simmer in a large saucepan over medium heat. Reduce the heat to low and slowly add the semolina flour in a steady stream, whisking constantly to prevent it from clumping. Continue to simmer, stirring until thick and creamy and begins to pull away from the sides of the pan, about 10 minutes.
Take off the heat, stir in the parmesan cheese and butter. Season with nutmeg, salt and freshly ground black pepper. Allow the mixture to cool slightly before adding the egg yolks. When cool, add the egg yolks and stir until well combined.
Lightly oil a half sheet pan. Spread the semolina mixture with an offset spatula into an even layer, about 1/2-inch thick. Let cool until fully set, about 40 minutes.
Preheat the oven to 350F. Layer the bottom of a baking dish with sauce. Using a ring mold, cut into 2-inch rounds. Layer the rounds in the baking dish, overlapping slightly. Generously grate the top with more Parmesan. Bake 25 minutes, until golden brown. I finished under the broiler for a few minutes to further brown the top. Garnish with fresh basil leaves if you like. Serve with extra tomato sauce on the side.