To prepare the roasted red pepper sauce: Preheat the oven to 400 degrees F. Set the peppers on a baking sheet and roast until the flesh is soft and the skin puckered, 35 to 45 minutes. Remove the peppers from the oven and put them in a bowl covered with plastic wrap. Set aside for 10 minutes to sweat. Remove the wrap, peel and seed the peppers. Cut the flesh into pieces and set aside.
Heat the oil in a saute pan. Add the shallot and cook until soft. Deglaze with white wine and cook 1 minute. Add the stock and the cooked red pepper. Cook 5 minutes. Cool slightly, and puree in the blender. Season with lemon juice, salt, and pepper, and transfer to a small saucepan to reheat in a few minutes.
To make the broccoli puree: Bring a pot of water to a boil. Cut the florets off the broccoli stem in even sizes. Peel the stem and thinly slice. Slice the leek into rings and rinse well.
Salt the boiling water, as for pasta, and add the broccoli and leek. Cook until very tender, about 10 minutes. Drain. Drop in the butter and puree with an immersion blender. Taste and adjust the salt. Add pepper, lemon juice and lemon zest, to taste. Serve the broccoli puree hot as a bed for fish.
To prepare the fish: Season the filets with salt and pepper. Heat the butter and oil in a skillet. Fry on both sides until golden and cooked through, about 4 minutes per side. Serve on a bed of broccoli puree with red pepper sauce alongside.
For the plate: Add a spoonful of broccoli puree to a plate and top it with the fish. Swirl the red pepper sauce around the plate and enjoy!