1. Heat the olive oil in a large pot over medium-high heat. When the oil is hot, add the onions and fennel. Stir to coat with oil and sauté, stirring occasionally, until it begins to color, about 5-6 minutes. Sprinkle some salt over it. Add the garlic cloves and tomato paste and stir well to combine. Cook this for another 2-3 minutes, stirring once or twice.
2. Add the red wine, stir well, and increase the heat to high. Boil until the liquid is reduced by half.
3. Add the Sambuca or other anise-flavored liquor, and the crushed tomatoes and olives.
4. Stir in the shrimp and bring the pot to a gentle simmer. Simmer for at least 1 hour.
5. Season to taste with salt and pepper: Add the chopped parsley and fennel fronds. Stir well to combine and serve over rice or pasta!