How to Make It
Preheat the oven to 375°. In a small roasting pan, toss the chicken thighs with the onion, leek, carrot and garlic. Add the olive oil and 1 1/2 teaspoons of the Madras curry powder and season with salt and pepper. Roast, turning once, until the chicken thighs are cooked through and the vegetables are tender, about 35 minutes. Let cool.
Meanwhile, in a medium saucepan, bring the milk to a simmer with the remaining 1 1/2 teaspoons of curry powder over moderately high heat. Remove from the heat and let cool.
In a food processor, pulse the chicken with the roasted vegetables until a puree forms. Season the puree generously with salt and pepper.
Melt the butter in a large skillet. Add the 3/4 cup of flour and cook over moderately low heat, stirring constantly, until lightly browned. Stir in the chicken puree. Gradually add the milk, little by little at first and whisking constantly until it has all been added. Cook over low heat, stirring constantly, until the mixture is no longer sticky, about 15 minutes. Season with salt and pepper and let cool to room temperature, about 1 hour.
In a large saucepan, heat 1 1/2 inches of vegetable oil to 350°. On a lightly floured work surface, roll the croquette mixture into 3/4-inch-thick ropes. Cut the ropes into 1 1/2-inch pieces.
In a shallow bowl, beat the eggs. Spread the bread crumbs in another shallow bowl. Dip the croquettes in the egg, then coat all over with the bread crumbs. Add the croquettes to the hot oil in batches, taking care not to crowd the pan, and fry until golden brown, about 1 minute. Transfer the croquettes to paper towels to drain and serve piping hot.