Sausage and Broccoli Rabe Torta

Ingredients:
2 large eggs
2/3 cup whole milk
1/2 cup all-purpose flour
1/4 teaspoon salt
3 tablespoons unsalted butter, melted
3/4 pound broccoli rabe
4 garlic cloves, finely chopped
1/2 teaspoon dried hot red-pepper flakes
3 tablespoons olive oil
3/4 pound sweet Italian sausage, casings removed
1/2 stick (1/4 cup) unsalted butter
1/4 cup all-purpose flour
1 3/4 cups whole milk
1/4 teaspoon salt
1/4 teaspoon black pepper
1 ounce finely grated Parmigiano-Reggiano (1/2 cup)
1 tablespoon unsalted butter, melted
1/4 cup dry bread crumbs
1/4 pound chilled Italian Fontina, coarsely grated (1 cup)
1 ounce finely grated Parmigiano-Reggiano (1/2 cup)
an 8-inch (20-cm) round springform pan

Instructions:
Blend together eggs, milk, flour, and salt in a blender until smooth. Transfer to a bowl.
Lightly brush a 10-inch nonstick skillet with melted butter and heat over moderate heat until hot but not smoking. Ladle about 1/4 cup batter into skillet, tilting and rotating skillet to coat bottom, then pour excess batter back into bowl. (If batter sets before skillet is coated, reduce heat slightly for next crespella.) Cook until just set and underside is lightly browned, about 30 seconds, then invert crespella onto a clean kitchen towel to cool completely. (It will be cooked on one side only.) Make 5 more crespelle with remaining batter in same manner, brushing skillet with melted butter as needed.
Cut off and discard 1 inch from stem ends of broccoli rabe, then coarsely chop remainder.
Cook broccoli rabe in a 6- to 8-quart pot of boiling salted water, uncovered, until just tender, about 5 minutes. Transfer with a slotted spoon to a large bowl of ice and cold water to stop cooking. Drain well in a colander and pat dry.
Cook garlic with red-pepper flakes in oil in a 12-inch nonstick skillet over moderate heat, stirring occasionally, until golden, about 8 minutes. Add sausage and cook, breaking up sausage with back of a wooden spoon, until no longer pink inside, about 5 minutes. Stir in broccoli rabe and cook, tossing to coat with sausage, until heated through, about 3 minutes. Remove from heat.
Heat butter in a 2- to 3-quart heavy saucepan over moderately low heat until foam subsides, then add flour and cook, whisking, 3 minutes. Add milk in a slow stream, whisking, and bring to a boil, whisking. Reduce heat and simmer, whisking occasionally, 5 minutes. Stir in salt, pepper, and cheese, then remove from heat.
Put oven rack in middle position and preheat oven to 425°F. Invert bottom of springform pan (torta will be easier to slide off bottom when serving), then lock. Wrap outside of entire bottom of springform pan with a double layer of foil. Generously brush inside bottom and side of pan with butter, then sprinkle bottom with bread crumbs.
Stir together Fontina and parmesan in a bowl. Put 1 crespella in bottom of springform pan, then sprinkle with one sixth of filling and drizzle with 1/3 cup sauce. Make 5 more layers each of crespella, filling, and sauce (end with a layer of sauce). Sprinkle cheese mixture evenly over top.
Bake, uncovered, until top is bubbling and golden, about 25 minutes. Cool in pan on a rack 15 minutes. Remove side of pan and carefully slide torta off bottom of pan onto a plate. Cut torta into wedges.