Season fillets with garlic powder, salt, and pepper. Place in vacuum-seal bag add 1 teaspoon olive oil, orange zest and fennel fond to the vacuum seal bag and seal with your vacuum sealer. If you don't have a vacuum sealer, use another air removal method.
Set up your immersion circulator in your water bath container and fill the water bath with water to in between the minimum and maximum fill lines. Heat the water bath with the immersion circulator to 130 degrees F
Add the sealed bag into water bath and secure with a clothes pin or weight. Cook for 30 minutes (45 minutes if frozen).
White sauce for fish
While fish cooks, heat 1 Tablespoon olive oil in a skillet over medium-high heat. Add fennel and cook 4 min, stirring occasionally. Add leek, garlic, orange zest, cook until soft about 2-3 minutes. When soft, add broth and ½ cup orange juice. Turn down the heat and simmer for 5 minutes
Stir in cornstarch slurry (1 tablespoon cornstarch + 1 tablespoon water). Simmer until thickened. Spoon the leek and fennel white sauce onto a platter.
Remove the fish from the water bath and bag. Discard fond and transfer fish over vegetable sauce, squeeze remaining orange juice over top, garnish with fennel fronds and toasted almonds.
For broccoli rabe:
Heat remaining oil in skillet over medium- high heat. Sauté garlic 30 seconds. Add broccoli rabe and sauté until tender, 5–6 minutes. Season with salt and pepper.
Notes
Skin On or Skin Off?
If using salmon in place of yellowtail, you might consider keeping the skin on. Sous vide salmon skin can be quite delicious if you sear it until crisp after cooking—think of it as salmon cracklings. But if you prefer your salmon skinless for any reason (say, if you're going to serve it simply poached, without searing), there's a much easier way to get rid of that skin than trying to cut it off before cooking: Just wait until after you've cooked it sous vide. The cooking process weakens the bond between skin and meat, making it very easy to peel it off gently with your fingers.Once the skin is removed, you can also very carefully flake off the dark brown flesh underneath if you'd like. There's no harm in eating it, but some people don't like the way it looks.