In a large dutch oven over low heat, cook onions in olive oil until translucent. This'll take about 15 minutes. Be careful not to let them brown.
Add the garlic, stir, and cook for and additional 2 minutes. Add the diced tomatoes, tomato sauce, seafood stock, water, brown sugar, and spices. Cover and simmer for an hour, stirring occasionally.
Stir in the shellfish and cook for an additional 10 minutes.
Notes
Serve on top of pasta with a crusty french bread.
Recipe by Iriemade at https://iriemade.com/cacciucco-tuscan-seafood-stew/