Preheat the oven to 325 degrees F. Prepare a mini muffin tin. Either use liners and spray with non stick cooking spray or spray muffin tins.
Bring a wide skillet 3/4 full of water to a low simmer.
Combine the butter, sugar, cocoas, and salt in a medium heatproof bowl and set the bowl in a wide skillet of barely simmering water. Allow the butter to melt and the mixture to become fairly hot, stirring every so often. Remove the bowl from the heat and allow the mixture to cool slightly.
Stir in the vanilla with a wooden spoon. Add the eggs one at a time, stirring vigorously after each one.The batter should look thick, shiny, and well blended. Stir in the flour, and pour the mixture into the prepared pan.
Bake for 11-13 minutes or until toothpick comes out slightly fudgy. Tops should still be a bit glossy. Let cool completely on a rack.