Step 1: Heat a large, heavy-bottomed skillet or Dutch oven over medium-high heat. Add the olive oil. Once shimmering, add the Italian sausage, breaking it up with a spoon as it cooks. Brown the sausage evenly for 5-7 minutes, until no pink remains. Remove the cooked sausage with a slotted spoon and set aside, leaving about 1-2 tablespoons of rendered fat in the skillet.
Step 2: Reduce the heat to medium. Add the chopped onion and sauté for 3-5 minutes, until softened and translucent. Add the minced garlic, fresh rosemary, and fresh sage. Cook for another minute, stirring constantly, until fragrant. Be careful not to burn the garlic.
Step 3: Pour in the chicken broth and diced tomatoes (undrained). Bring the mixture to a gentle simmer, scraping up any browned bits from the bottom of the pan with a wooden spoon. This deglazing step adds a tremendous amount of flavor.
Step 4: Stir in the rinsed cannellini beans and the cooked Italian sausage. Season with salt and black pepper to taste. Continue to simmer for 10-15 minutes, allowing the flavors to meld and the sauce to thicken slightly. If the sauce becomes too thick, you can add a splash more broth.
Step 5: If using, stir in the baby spinach until it wilts, which typically takes just 1-2 minutes. Taste and adjust seasonings as needed. A sprinkle of red pepper flakes can add a lovely subtle heat if desired.
Step 6: Ladle into bowls and garnish with fresh parsley and a drizzle of extra virgin olive oil. Serve hot and enjoy.