Crab Stuffed Salmon

INGREDIENTS:

1/2 bunch fresh parsley
10 Ritz or butter crackers (about 1 ounce)
4 (about 6-ounce, at least 1-inch thick) skinless salmon fillets
4 teaspoons Old Bay seasoning, divided
1 tablespoon olive oil
1/2 medium lemon
2 tablespoons mayonnaise
1 tablespoon whole grain mustard
1/2 teaspoon freshly ground black pepper
8 ounces jumbo lump crab meat
FOR THE SAUCE (OPTIONAL):
8 tablespoons (1 stick) unsalted butter
1/2 medium lemon
3 large egg yolks
2 teaspoons Dijon mustard
1/2 teaspoon whole grain mustard (optional)
1/4 teaspoon kosher salt
1/8 teaspoon cayenne pepper (optional)

DIRECTIONS:

Arrange a rack in the middle of the oven and heat the oven to 350°F. Line a rimmed baking sheet with parchment paper.
Pick and finely chop the leaves from 1/2 bunch fresh parsley leaves until you have about 1/2 cup. Place 10 Ritz crackers in a small zip-top bag, press out the air, and seal the bag. Crush the crackers a rolling pin or bottom of a saucepan into crumbs (about 1/3 cup).
Pat 4 skinless salmon fillets dry with paper towels, then place on the baking sheet. Starting 1 inch from one end, cut a slit down the center of each fillet lengthwise, cutting all the way through to the bottom and stopping 1 inch from the other end to make a pocket. Season the salmon with 2 teaspoons of the Old Bay seasoning and 1 tablespoon olive oil, then rub to distribute evenly on all sides of the salmon.

Squeeze the juice of 1/2 medium lemon into a medium bowl until you have 1 tablespoon. Add the remaining 2 teaspoons Old Bay seasoning, 2 tablespoons mayonnaise, 1 tablespoon whole grain mustard, and 1/2 teaspoon black pepper. Stir until well combined. Drain 8 ounces jumbo lump crab meat (about 2 cups). Add the crab, cracker crumbs, and half of the parsley. Fold until well combined. Stuff the filling into the salmon pockets (about 1/2 cup each).
Bake until the salmon registers 120º F on an instant-read thermometer for medium rare. Meanwhile, make the sauce …