In a food processor, pulse bread until large crumbs form (you should have about 6 cups); season with salt and pepper. Set aside.
Preheat oven to 375 degrees. In a 6-quart heavy-bottom saucepan, cook sausage, onions, and garlic, stirring occasionally, until onions are translucent and sausage is starting to brown, 15 to 20 minutes.
Add tomato paste, broth, wine, thyme, and 2 cups water; bring to a boil. Reduce to a simmer; add beans. Simmer, stirring occasionally, until slightly thickened but still soupy, about 10 minutes.
Stir in 2 cups of the breadcrumbs. Divide sausage mixture between two 3-quart shallow baking dishes or eight 10-ounce ramekins. Top with remaining breadcrumbs.
Bake, on a baking sheet, until topping is golden, 30 minutes.
To freeze the casserole, prepare the recipe through step 4; cool completely, then cover tightly with plastic wrap (label and date), and freeze up to three months.
To cook frozen casserole: Bake without thawing in an oven heated to 375 degrees, covered with foil, until bubbly and hot in the center, about 1 hour. Remove foil; continue baking until breadcrumbs are golden brown, 15 to 20 minutes more.