Clean mussels by scrubbing and removing beards. Discard any cracked or open mussels.
Sauté shallots and garlic in olive oil and butter until fragrant and softened.
Add grape/cherry tomatoes, cook until they soften, then pour in white wine. Simmer briefly.
Add cleaned mussels, season with dried thyme and sea salt, and cover to cook until they open. Discard any unopened mussels.
Sprinkle with chopped parsley, then serve mussels and broth in bowls with whole-wheat sourdough bread on the side.