This gratin is very nearly one-dish, very good, and very easy. This is from Kathy Brennan's and Caroline Campion's Keepers.
2/3 cup panko or regular dried breadcrumbs
2 tablespoons unsalted butter, melted
2 tablespoons olive oil
1 pound sweet Italian sausages, casings removed
1 small yellow onion, chopped
4 garlic cloves, minced
1 heaping tablespoon tomato paste
1 scant tablespoon fresh thyme leaves or 1 scant teaspoon dried
1/2 cup dry white wine
1.5 cups low-sodium chicken broth
Two 15.5-oz cans white beans, such as cannellini or Great Northern, drained and rinsed
4 large handfuls of baby spinach (optional)
Preheat oven to 425, with a rack in the middle position. In a small bowl, combine panko and butter, season with salt and set aside.
In a large skillet, heat the oil over high heat until it shimmers. Add the sausages and cook, stirring often and breaking up the meat, until browned, about 4 minutes. Leaving as much of the oil in the pan as possible, transfer the sausage to a medium bowl and set aside.
Reduce the heat to medium-low, add the onions and garlic and cook, stirring occasionally, until the onions are softened, about 8 minutes. Add the tomato paste and thyme and stir for about 30 seconds. Add the wine and briskly simmer, scraping up any caramelized bits from the bottom of the pan, until almost evaporated, about 2 minutes.
Add the broth and bring to a simmer, then add the beans, cooked sausage, and any juices. Season with salt and pepper and simmer, stirring occasionally, until heated through and some of the liquid is absorbed, about 5 minutes. The mixture should be wet, but not drowning in liquid. Off the heat, stir in spinach (if using). Check the seasonings, then transfer the mixture to a 3-quart baking or gratin dish.
Top evenly with the panko mixture and bake until bubbling and the top is golden brown, about 15 minutes. Let rest for 5 to 10 minutes before serving.