1. Preheat the oven 325 degrees. Grease and flour a 12-cup standard muffin tin.
2. In a large heavy saucepan over medium heat, begin melting the butter, stirring occasionally. When its half melted, add the chocolate and continue cooking until the chocolate is half melted. Remove from the heat and continue stirring until mixture is smooth.
3. Mix in the sugar, vanilla, eggs and salt until smooth. Mix in the flour, just until blended.
4. Ladle the batter into the muffin tin, filling each cup about three-quarters full. Bake for 15 minutes until the edges are set but the centers are still very wet and sunken. Cool on a rack for 5 minutes. Run a knife around the edge of each cupcake and carefully remove to a cooling rack. Cool for 10 minutes more. Serve warm.