Start the Seafood Vol-au-Vent by baking off the "puss pastry shells" as per the instructions on the box. Remove from the oven and let them cool while you prepare the filling.
Melt the butter in a skillet or large saucepan on medium heat. Whisk in the flour, Old Bay seasoning and salt. Mix continuously until the "roux" becomes smooth and simmer for a minutes.
Keep whisking while slowly adding the milk. Make sure whisk the sauce until smooth before adding more milk to the pan. Cook the "bechamel" sauce until it simmers and thickens.
Add the finely chopped garlic and fresh dill into the bechamel sauce. Squeeze in the fresh lemon juice and stir everything in the sauce.
Make sure that the frozen shrimp and scallops are thawed out and drained of any liquid. Drain the can of crab meat, and add all of the seafood to the sauce. Cook the seafood in the sauce if not already cooked.
Fold the peas into the seafood filling, bring back to a simmer and then take the pan off the heat.
Use a knife to carefully remove the tops from the baked vol-au-vents. Fill the Vol-au-vent shells right before serving so that the shell stays crispy, and the filling warm. Place the cut out tops over the filling as a "hat" Serve any extra filling on the side.