Brown the Sausages: In a heavy saucepan or cast iron pot, heat the olive oil over medium heat. Once hot, add the sausages and cook until golden brown on all sides. Remove the sausages and set aside.
Sauté Aromatics: Add a little more olive oil to the pan if needed. Add the chopped onion, minced garlic, and thyme. Sauté for about 5 minutes, until the onions are soft.
Deglaze and Simmer: Pour in the white wine, chicken stock, and butter beans. Bring to a simmer and cook for about 5 minutes to allow the alcohol to evaporate.
Combine Ingredients: Add the spinach, crème fraîche, lemon zest, most of the breadcrumbs (reserving 2 tablespoons for topping), and parmesan cheese. Stir until the mixture is smooth and creamy.
Finish Cooking: Return the sausages to the pot, nestling them into the casserole. Cover with a lid and cook for another 5 minutes to heat through.
Top and Serve: Remove the lid, sprinkle the remaining breadcrumbs, extra parmesan, and a drizzle of olive oil on top. Serve hot, divided between bowls.