In a large skillet, toast the coriander seeds over moderately high heat until fragrant, about 2 minutes. Transfer the seeds to a mortar and let cool. Crush the seeds coarsely with a pestle.
In the same skillet, heat the olive oil until shimmering. Season the chicken drumsticks with salt and pepper, add them to the skillet and cook over moderately high heat, turning, until golden brown all over, about 10 minutes. Add the onion and cook, stirring occasionally, until softened, about 3 minutes. Add the garlic and cook for 1 minute. Add the broth and crushed coriander and bring to a boil. Cover and cook over moderately low heat until the chicken is cooked through, about 15 minutes.
Transfer the chicken to a platter, cover and keep warm. In a small bowl, whisk the mustard with the crème fraîche and tarragon. Whisk the mixture into the skillet and simmer the sauce over moderate heat until thickened, about 5 minutes. Return the chicken to the skillet and turn to coat. Serve the chicken with crusty bread.