Preheat oven to 325 degrees F. Line an 8 inch square baking pan with foil and grease foil.
Whisk together the flour, baking soda and salt; set aside.
Put 1 cup (6 oz) chocolate chips in a heat proof mixing bowl and set next to the stove.
In a saucepan, stir together the softened butter, sugar and water. Set over medium heat and bring just to a boil. Remove from heat and pour hot sugar mixture over the chocolate chips, scraping saucepan to get all sugar mixture (I use a silicone scraper). Stir until chips are melted and mixture is smooth.
Add one of the eggs and stir with a heat proof scraper (or whisk) until blended. Add the second egg and stir until blended. Stir in the vanilla.
Add the flour mixture and stir until blended.
If the mixture is very hot, let it cool for about 5 minutes, then add the remaining 1 cup of chips.
Pour mixture into the prepared metal pan and bake at 325 for 35-40 minutes.
Let cool completely, then lift from pan and cut into squares.