Cut the eel into 2 1/2-inch lengths. Place 1/4 cup of the flour in a plastic bag and toss the eel pieces until lightly floured. Melt 1 tablespooon of the butter in a flameproof casserole or dutch oven and gently fry the eel until golden, about 5 minutes. Add the brandy, wine, and bouquet garni. Season with salt and pepper. Bring to a boil and cook for 3-4 minutes. Remove the eel to a serving platter with a slotted spoon and keep warm. Reduce the heat and simmer the cooking liquid for 20 minutes. Stir the mushrooms into the sauce and cook for 15 minutes longer. Melt 1 tablespoon of the remaining butter in a skillet and cook the onions until golden, shaking the pan occasionally. Sprinkle the sugar over the onions and continue cooking until caramelized. Season with salt and pepper. In a small bowl beat together 2 tablespoons of the butter and 2 tablespoons of the flour to obtain a paste. Drop the paste by teaspoon, a little at a time, into the cooking liquid and boil until thickened. Return the eel to the sauce and simmer for 10 minutes. Stir in the onions and heat through. Heat the oil in a skillet and fry the bread triangles over moderate heat until golden, turning frequently. Drain on paper towels. Serve the stew in a deep-dish platter, surrounded by the croutons.
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4 1/2 lb eel, skinned
3 cups Riesling or Chenin Blanc wine
1/2 cup Armagnac
20 pearl onions, peeled
1/2 lb mushrooms, quartered if large
1/2 cup unsalted butter
1/4 cup + 2 tbsp flour
1 tbsp sugar
1/4 cup cooking oil
6 slices white bread, crusts removed and cut into triangles