Preheat a sauté pan over medium high heat. Add butter and melt, do not brown. Add shrimp, garlic, shallot and saffron; sauté just until shrimp become opaque. Add tomato and scallions, sauté briefly. Deglaze with white wine. Allow liquid to simmer and reduce by 1/2. Add cream simmer until sauce thickens slightly. Season with lemon juice, salt and pepper. Finish with chopped parsley. Portion shrimp onto warm serving plates or a platter and top with sauce.