In a large pan, melt the butter. Add the onions and scallions and cook until the onions are translucent, 5 to 8 minutes. Add the cream cheese, sour cream and fresh lemon juice and whisk until creamy and smooth.
Mix in the crawfish, vermouth, hot sauce, cayenne and Creole seasoning. Cook for 10 minutes over low heat, stirring constantly to prevent scorching.
Let cool and then refrigerate until ready to serve.