In a medium saucepan combine sugar and 1/4 cup water. Cook over moderate heat gently swirling pan until sugar dissolves, and mixture is clear. Now cook, undisturbed until it is a golden amber color about 5 minutes. Do not leave it it will burn quickly, so just watch it .Remove saucepan from heat and carefully whisk in butter, it will bubble up, whisk constantly, and slowly drizzle in warm milk until blended, it may look to seperate a little., that is fine. Slowly whisk in the egg mixture and bring to a boil, stir at all times, bring to a boil over medium heat.and stir until thickened, about 2 minutes. Stir in the vanilla and and sea salt. Strain the custard through a fine mesh strainer into a heatproof bowl. Place a piece of plastic wrap directly on the surface of the custard and refigerate until completely chilled.