3 slices crustless white bread, torn into small pieces
9 tbsp. unsalted butter, melted
Kosher salt, to taste
8 oz. hollow pasta, preferably elbow macaroni
1⁄4 cup flour
3 cups milk
4 cups grated graviera or kefalotyri cheese (about 12 oz.)
3⁄4 tsp. ground cinnamon
1⁄8 tsp. freshly grated nutmeg
Freshly ground black pepper, to taste
2 tbsp. extra-virgin olive oil
8 large shallots, finely chopped
16 oz. baby spinach, roughly chopped
8 scallions cut into 1⁄4"-thick rounds
1⁄3 cup roughly chopped fresh dill
1 3⁄4 cups crumbled feta (about 8 oz.)