For the almond vinaigrette
Place almonds in zipper-lock bag and pound with roiling pin until coarsely crushed. Whisk crushed almond, shallot, vinegar, honey, and mustard in medium bowl. Whisking constantly, drizzle in olive oil. Whisk in water and tarragon and season with salt and pepper to taste.

For the salmon
Use sharp
knife to remove any whitish fat from belly of salmon and cut each fillet into  equal pieces. Using sharp (or serrated) knife, cut 4 shallow slashes, about 1 inch apart, through skin of each fillet (do not cut into flesh). Pat salmon dry with paper towels and rub with oil. (Prepped salmon can be refrigerated for up to 24 hours before cooking.)
Adjust oven rack to lowest position, place a rimmed baking sheet on rack, and heat oven to 500ºF. Season salmon with salt and pepper. Reduce oven temperature to 275ºF and remove hot baking sheet. Carefully lay salmon, skin side down, on hot sheet. Roast until center is still translucent when checked with tip of paring knife and registers 125ºF (for medium-rare), 9 to 13 minutes.
Transfer fillets onto individual plates or platter, spoon vinaigrette over top, and serve.