Season the salmon fillets generously with kosher salt on all sides.
Place the salmon in a single layer in a gallon-size Ziploc bag, adding olive oil and optional aromatics. Seal the bag, leaving it to rest in the refrigerator for 30 minutes to overnight.
Preheat your water bath using an immersion circulator You’ll want to set your sous vide to 125°F for medium-rare or 130°F for medium. If you like it a little firmer, you can go up to 135°F, but I wouldn’t go much higher. Then, using the water displacement method, remove the air from the bags and cook the salmon for 30 to 45 minutes for fillets up to 1 inch thick, or 45 minutes to 1 hour for thicker fillets.
Once cooked, carefully remove the salmon from the bags, discard the aromatics, and gently blot the salmon dry with paper towels.
For immediate serving, peel away the skin and present the skinned side down. For cold serving, chill the salmon in the refrigerator and use as desired. To sear, heat vegetable oil in a skillet and cook the salmon until the skin is crisp, then serve.