Heat the butter in a large Dutch oven or pot over medium-high heat. Add the curry powder and cook, stirring, 30 seconds. Add the onion, celery, shallots, garlic, 1/2 teaspoon salt, and pepper to taste; cook until the vegetables are translucent, 4 to 5 minutes. Add the wine and 1/4 cup water and bring to a boil over high heat. Stir in the mussels; cover and cook, shaking the pot occasionally, until the mussels open, 3 to 5 minutes. Transfer the open mussels to a bowl using a slotted spoon (discard any that do not open). Cover the bowl and set aside.
Add the cream to the pot with the cooking liquid and vegetables; bring to a boil and cook until reduced by half, 5 to 8 minutes. Stir in the cognac and lemon juice. Return the mussels to the pot and stir to coat with the sauce. Serve with the lemon wedges and toasted baguette slices.
Photograph by Christopher Testani
Recipe courtesy Food Network Magazine