Serve this warm and hearty soup with toasted pieces of baguette.
In a large soup pot, heat the olive oil over medium heat. Add the leeks and fennel and cook until wilted and fragrant, 4-5 minutes. Add the garlic and cook 1 minute more.
Stir in the tomato paste and cook for 2-3 minutes, until the tomato paste begins to brown slightly.
Add the white wine, broth, and crushed tomatoes and bring to a simmer over medium low heat. Simmer until good flavor develops, 25-30 minutes.
Stir in the olives, shrimp, mussels, and broccoli rabe, ensuring it is all submerged in the broth. Cover the pot and simmer over medium low heat until the shrimp is pink and opaque, the mussels are open, and the broccoli rabe is tender-crisp, 4-5 minutes. Season the soup with salt and pepper.
To serve, ladle the soup into bowls and garnish with additional freshly ground black pepper, a sprinkling of fresh herbs, and a bit of lemon zest. Serve with toasted bread.