In a large saucepot on medium heat, sauté garlic and shallots in oil and butter until soft. Add the mussels and wine. Increase to high heat and cover pot with a lid, shaking a few times. Remove mussels from pot when shells are fully opened and drain in a colander to cool. Loosen mussel meat from shells and place mussels in the half shell in a shallow pan and refrigerate until ready to marinate.
Place mussel juice (from cooking) back on the heat and reduce by one third. Remove from heat and allow to cool.
In a small bowl combine and whisk together the vinegar with the mussel juice. Add tomato concasse, and fresh herbs. Pour over mussels and refrigerate for at least 1 hour.