In a stainless steel pot, bring all ingredients for the poaching liquid to a boil, then immediately set aside to steep and cool. When the poaching liquid reaches 115 degrees, add the salmon and let stand to allow it to cook until the fillet is opaque and begins to flake (approximately 7-10 minutes).
To prepare the vinaigrette, combine vinegar, coriander, mustard seeds, mustard, honey, shallot and lemon thyme leaves in a blender. Then, on low speed, slowly incorporate the hazelnut and extra virgin olive oil to emulsify. This vinaigrette can be placed in tightly sealed container and stored in the refrigerator for up to one week.
To make the rillettes, remove salmon from the poaching liquid, trim off all skin, grey, and flake into a non-reactive bowl. Fold in the smoked salmon. Add 6 tablespoons of the vinaigrette to the flaked salmon, gently toss and reserve.
To plate, place a quenelle of rillettes on each crostini, garnish with watercress, grapefruit, golden trout roe, pickled red onion and edible flowers.