Prepare Bechamel and keep warm. Add to the sauce all of the cheddar and half of the Grana and salt and pepper to taste, mixing to melt and incorporate cheese. Add cooked pasta. Mixture will be wet and hot.
Grease an 11x18 pan with butter and spread breadcrumbs evenly. Pour in pasta and top with remaining cheeses.
Cook in a water bath at 425 degrees for 15 to 20 minutes or until brown and bubbly. Let cook slightly before serving.
***NOTE*** The eggs are incorporated with the cooked pasta with the béchamel sauce and first half of the cheese. You need to be sure the pasta is not too hot so as not to cook the eggs. But once the pasta is poured into the mold the béchamel sauce is poured over the top of the pasta and mixed in by hand as the first half of the cheese is sprinkled in and incorporated by hand as well. Then one by one add the eggs, incorporating them evenly, by hand, throughout the mixture. Once evenly mixed, top with the remaining cheese and place in a water to cook until golden brown.
For the Bechamel Sauce:
Melt butter in a large saucepan over medium heat. Once melted, stir in the flour until smooth. Continue stirring as the flour cooks to a light, golden, sandy color, about 3 or 4 minutes.
Increase heat to medium-high and slowly whisk in milk until thickened by the roux. Bring to a gentle simmer, then reduce heat to medium-low and continue simmering until the flour has softened and no longer tastes gritty, approximately 7 to 10 minutes, then season with salt and nutmeg.