Flounder, beloved for its fine texture and delicate flavor, is one of the many popular flat fishes to be found at the market, where it is most often presented in fillets.  Delicate indeed. This is not the fish of choice for cioppino or fish Veracruz, as it can't fend off tomato sauces or robust seasonings as it falls apart in the pot.  It bakes nicely though—holding together in the process but falling apart with the slightest encouragement when done.  Every night in a thousand restaurants, sheet pans of flounder, sole and halibut fillets are baked off for individual servings. 

But why not stack and bake fish fillets on top of each other, present the whole dish to guests and then divide it up and serve it like so much lasagna?  "Well," you say, "You need a filler or stuffing.  After all, there is more to lasagna than pasta,"  What to use?  We agree that tomatoes are out.  Instead, something light in texture, taste and seasoning is needed to separate and compliment the fish.

So here we have three fillets of flounder layered with shrimp mousseline.  Hereafter, “shrimp filling.”  The shrimp can be very finely diced with a chef's knife but a food processor works best.  But, either way, get the puree in an ice bath for the rest of its journey.
 

TIP:  Shrimp (all fish) need to be very cold, and stay cold, whenever you are making a puree out of them.

Herbes de Provence is quite mild if not used to excess, or go with your own combination of thyme, oregano, etc.  So too with the shallots, don't use yellow onions here.  The red bell peppers are needed for color. The bread crumbs for color and texture. 
 
 

Stacked Fillets of Flounder with Shrimp Filling
Yield:  4 servings 
See Abbreviations, if needed
For the filling:
  ·   10          raw shrimp, medium size 
  ·   1-2 T     herbes de Provence, or seasoning of choice
  ·   S/P        to taste, but quite generous
  ·   ½ C       finely diced red bell pepper
  ·   1/3C      finely diced shallots
  ·   1            egg white
  ·   ½ C       breadcrumbs or Panko (Japanese breadcrumbs)

1.  Place cleaned and paper-towel-dried shrimp in 
     a food processor and pulse very briefly with the steel blade 
     to break up the shrimp into a course puree.  Do not pulse to a smooth mush
2.  Turn out the pureed shrimp into a stainless steel bowl and place it into 
     a larger bowl filled with ice 
3.  Add the seasonings, diced red peppers and shallots to the iced shrimp
     puree and mix all gently with a fork. (Hold 2T of the peppers in reserve)
4.  Add the egg white and mix thoroughly
5.  Fold in the breadcrumbs and set aside, still on ice
For the dish:
  ·   3          flounder fillets (nice size, not too thin, about ¾ lb each)
  ·   2T       EVOO
  ·   1/3C    bread crumbs or Panko

1.  Preheat oven to 350F
2.  Select a casserole pan or gratinée large and high enough to hold 
     a stack of flounder fillets (three high).  Oil the pan
3.  Place one fillet in the pan and spread a layer of the 
     shrimp filling on top using a spatula or broad knife
4.  Add a second fillet and cover it with the rest of the shrimp filling
5.  Add a third and final fillet, brush it nicely with EVOO and top generously 
      with bread crumbs
6.  Garnish the top of the flounder filet stack with the reserved diced red peppers
7.  Bake until the filet stack is cooked through, about 25 minutes
8.  Serve with a cooked green vegetable of the season