In the skillet, melt the remaining 3 tablespoons of butter. Add the shallots and garlic and cook over moderate heat, stirring occasionally, until softened and just starting to brown, about 5 minutes. Add the wine and Cognac and simmer until slightly reduced, about 2 minutes. Stir in the tomatoes, tomato paste and cayenne and simmer for 5 minutes, stirring occasionally. Add the shrimp and cook, stirring, until just cooked through, 3 to 5 minutes. Stir in the crème fraîche; season with salt and pepper. Serve with bread.