For the potato puree: Cook the potatoes in salted water until tender. Drain and cool until you can handle them. Peel and place in a blender.
Add 1/2 cup of the broth, cheese, cream, butter, salt and pepper. Process until you have a creamy texture, adding the remaining broth as needed. Set aside.
For the lemongrass sauce: In a saucepan over low heat, infuse the cream, the fish stock, lemon grass, and saffron for 5 minutes.
In another pan heat the oil and butter. Add the garlic and cook until it begins to brown. Add the white wine, herbs, and cayenne pepper. Cook until this sauce is reduced to half.
Add the flour and mix well. Whisk for two minutes to cook out the raw taste in the flour. Add the shrimp shells and allow them to infuse a little, then slowly begin adding in the cream and stock mixture. Cook over low heat for about 10 minutes. Strain and add a pinch of salt and pepper.
For seasonal vegetables: Heat the olive oil in a large skillet. Add all the vegetables and cook, stirring. Season with the lemon, white wine, and a small pinch of salt. Add the chives.
For the trout: Season the fish with salt and pepper. Add enough olive oil to a large nonstick skillet to coat and heat over medium-high heat. Cook the fish until just cooked through, about 2 minutes on each side.
To assemble the dish: On a hot, flat square plate, make a thin pool of puree in the center, top with a trout fillet diagonally. Spread the lemongrass sauce on one side of the fish and finish with the sauteed vegetables on top and around the trout. Garnish with some fresh shoots.