DIRECTIONS
Melt 3 TBSP. butter in a medium saucepan.
Add the shallots; cook until softened.
Sprinkle in the flour; cook, stirring until the roux is fragrant. Do not let it brown.
Take the pan off the heat; whisk in the milk, making sure to dissolve all the roux.
Season with salt and pepper and return to heat.
Bring to a simmer, stirring often; reduce heat to low and simmer until the sauce is thickened.
Stir in the mustard, lemon juice and parsley.
Season with white pepper and cayenne; check for salt.
Fold in the crab; scrape the mixture into a bowl.
Place on ice to cool quickly.
Melt the remaining 5 TBSP. butter.
Brush 6 individual gratin dishes (2 cup capacity) with the butter.
Divide the crab stuffing among the gratins, mounding in the center.
Cut the flounder fillets each in 4 pieces.
Place over the stuffing in each dish, covering completely.
Brush fish with remaining butter and bake at 450 degrees on top rack of oven.