1
In a container or zip-top bag, combine the dill, garlic, vinegar, mustard and salmon. Marinate for 4-6 hours.
2
Preheat the oven to 375°F.
3
On one baking sheet, toss the potatoes with 2 tablespoons oil and a big pinch of salt and pepper. Roast for 15-20 minutes, until the potatoes are crisp.
4
On a second baking sheet, toss the pearl onions with 1 tablespoon oil, balsamic and a pinch of salt and pepper. Roast for 12-15 minutes, until softened.
5
Remove the salmon from the marinade, dry with paper towels and sprinkle with salt and pepper. Heat a large skillet over medium heat with the remaining 1 tablespoon oil. When hot, add the salmon skin side-up. Sear until golden brown, then transfer to a baking sheet and finish cooking in the oven for 8-10 minutes.
6
In a bowl, whisk together both of the mustards, garlic, heavy cream, vinegar, sour cream, olive oil, lemon zest, lemon juice, salt and pepper until emulsified. Adjust the seasoning to taste.
7
In a blender, purée the parsley, dill, garlic and vinegar. With the motor running, drizzle in the oil until emulsified. Season to taste with salt.
8
In a medium bowl, toss the celery and tomatoes with the parsley dressing to coat.
9
To serve, divide the roasted onions and potatoes between plates. Top with salmon fillets, tomato salad, and mustard dressing.