Preheat oven to 400º. Line an 8-inch square metal baking pan with nonstick foil.
Melt butter and chocolate in the microwave stopping every 30 seconds to stir. When almost completely melted, stir until smooth.
Stir in sugars, vanilla, and salt.
Stir in eggs one at a time, followed by the flour. Stir until very smooth, about 1 minute, until the mixture pulls away from the sides of the bowl.
Spread batter in prepared pan and bake for 20 minutes.
Prepare a water bath. Pour ice water into a large roasting pan or kitchen sink to a depth of about 1 inch.
Remove pan from oven and place in a water bath...avoid getting any water on brownies. Let cool completely, then lift out and cut squares.
