Seafood Appetizer Bread with Crab and Shrimp

loaf of long French bread

unsalted butter

all purpose flour

milk , heated

kosher salt

freshly cracked black pepper

Parmesan cheese

slices of Swiss cheese

egg yolk , beaten

unsalted butter , softened at room temp

crabmeat , well drained

cooked small salad shrimp

parsley , chopped

pepper jack cheese , grated

green onion , chopped, for garnish, optional