Preheat oven to 375°F (190°C).

Melt 2 tablespoons of butter in a saucepan over low heat.

Slowly stir in flour to make a smooth paste and heat gently.

Remove from heat and add Dijon mustard and salt.

Slowly add milk, stirring continuously to avoid lumps.

Place the saucepan over medium heat.

Cook, stirring constantly, until the mixture thickens.

Set aside the sauce to cool completely. (It will become firm).

In a separate bowl, combine shrimp, crab meat, Swiss cheese, hard-cooked egg, shallots, parsley, green onion, minced garlic, and sour cream.

Gently fold the cooled sauce into the seafood mixture.

Lay one sheet of phyllo pastry on a baking sheet.

Brush with melted butter and sprinkle with bread crumbs and Parmesan cheese.

Repeat layering with the remaining phyllo pastry sheets, butter, bread crumbs, and Parmesan cheese.

Spread the seafood mixture evenly over the phyllo pastry.

Carefully fold the sides of the phyllo pastry over the filling, then roll up the strudel.

Brush the top of the strudel with melted butter.

Bake for 30 minutes, or until golden brown.

Let cool slightly before slicing and serving.

Garnish with parsley, shrimp, and lemon slices.