1. Preheat the oven to 425ºF and line a baking sheet with parchment paper.
2. Combine crème fraiche and Dijon mustard in a lidded glass bowl. Gently and generously coat each salmon piece with the crème fraiche mixture. Cover and refrigerate in the sauce, at least 20 minutes.
3. To prepare the coulis, mince garlic and shallot and set aside.
4. Bring a medium pot of water to boil and blanche that tomatoes 10-15 seconds, just long enough for the skin to begin to split.
5. Cool the tomatoes briefly in a bowl of ice water, then remove them to a cutting board. Core the tomatoes, slip off the peels and halve them across their “equators.”
6. Using your thumb, gently remove as many seeds as possible from the pockets exposed by halving the tomatoes, then cut into ½-inch pieces.
7. Heat olive oil over medium-low heat. Add garlic and shallot and “sweat” for 3 to 4 minutes, being careful to soften the vegetables without browning them.
8. Add the tomato pieces and increase the heat to medium-high. Simmer the tomatoes as they cook down until they’ve formed a thick, reduced sauce, 10 to 12 minutes, stirring occasionally.
9. Remove tomatoes from the heat, add the thyme leaves, salt and pepper to taste and (carefully) blend to a purée with an immersion blender or traditional blender. Check seasoning again and set aside off the heat until the salmon is done.
10. Remove salmon from the refrigerator and gently place on the parchment-lined baking sheet. Roast for 10 to 12 minutes, until the marinade has cooked.
11. Pool a generous serving of sauce on each plate, top with salmon portions and top with freshly grated lemon zest, garnishing each plate with a few sprigs of fresh thyme if desired.