In a colander, wash mussels well, place in a bowl, and let sit in the refrigerator until ready to use.
In a large saucepan or dutch oven, heat garlic over medium-high heat.
Add in leeks and garlic. Sauté until leeks turn translucent, about 2-3 minutes.
Add in the rest of the ingredients and stir until well combined. Bring to a boil over medium-high heat. Once at a boil, reduce heat to medium-low and let simmer for five minutes, or until the alcohol has cooked out.
Over high heat, bring the sauce back to a boil. Add in cleaned mussels, stir, and cover. Give the pan a shake while covered and let steam for 2-3 minutes. Remove the lid and give the mussels a stir. If all of the mussels have opened, take the pan off of the heat and pour mussels and sauce into desired serving dish. Be generous with the sauce! If not all of the mussels have opened, cover and cook for an additional minute, or until opened.
Top with fried shallots and sausage if using. Serve warm!