In the stockpot, sweat the garlic, leeks, and salt in the olive oil until softened over medium-low heat. Place the mussels in the colander and spray them with cold water to remove any excess dirt or grit. Remove any beards with a pair of needle-nose pliers.
Add the chopped tomato and the wine to the stockpot and turn the heat to medium high, and bring to a simmer. Insert the colander of mussels into the stockpot and cover. After 3 minutes, check to see if the mussels have opened. If some are still closed, cover the pot, and cook for an additional 30 seconds. Discard any unopened mussels.
Place the mussels in a serving bowl. Remove 10 mussels from their shells and add them to the stockpot. Using a stick blender or a bar blender, puree the mussels until the liquid is of a sauce-like consistency.
Pour the sauce over the mussels and garnish with chopped parsley. Serve with a loaf of crusty bread.