• Heat your oven to 350°F. Line a baking sheet with parchment because nobody wants to scrub crusty seafood off a pan later.
• Grab your salmon fillets and pat them dry with paper towels. Now do that slicing thing I mentioned earlier - cut a slit down the center lengthwise, starting 1 inch from one end and stopping 1 inch from the other end. You're creating a little pocket for all that crabby goodness.
• Season those gorgeous fillets with 2 teaspoons of Old Bay and the olive oil. Rub it all over like you're giving the salmon a little spa treatment.
• Now for the filling: In a bowl, mix 1 tablespoon lemon juice, the remaining 2 teaspoons Old Bay, 2 tablespoons mayo, 1 tablespoon whole grain mustard, and the black pepper. Stir it up.
• GENTLY fold in the crab meat, cracker crumbs, and half the parsley. Remember what I said about treating that crab like it's made of gold? Because it basically is, price-wise.
• Stuff about 1/2 cup of filling into each salmon pocket. Don't worry if it looks messy - it'll still taste amazing.
• Bake until the salmon hits 120°F on a thermometer for medium-rare, which should take about 15 minutes but honestly depends on how thick your fillets are and whether your oven runs hot like mine does (why do they never tell you that in recipes??).

While that's happening, you can make the sauce if you're feeling ambitious:

• Throw the lemon juice, egg yolks, Dijon, whole grain mustard (if using), salt, and cayenne (if using) into a blender.
• Blend for like 5-10 seconds.
• With the blender still running, sloooowly pour in the melted butter. It should get all pale and creamy and emulsified. If you don't know what emulsified means, it's that magical moment when everything comes together and looks smooth instead of separated and gross.
• When the salmon's done, drizzle that sauce over the top and sprinkle with the remaining parsley to make it look like you really know what you're doing.