In a small pot, place the water and heat it to boil.
In a heat resistant bowl, put the two types of chocolate and butter, and place this on top of a pot wth boiling water in it, for the chocolates to melt.
In a different bowl, beat the eggs, sugar and vanilla until this mixture lightens and gets fluffy, you should be able to make an number eight with the resulting batter.
Add the melted chocolate to the mixture and mix until well incorporated.
Lastly, add in he flour and salt, previously sifted or until it is all well integrated.
Bake in Individual molds (ramekins) or cupcake molds previously greased at 350°F for 10-12 min. (it is important not to go over this time, otherwise the lava cakes will fully cook).
Serve right after ready and dust confectioners sugar on top.