Don’t preheat oven yet because dough requires chilling.
In bowl of a stand mixer, thoroughly mix together the flour, salt and baking soda. Add the sugar and powdered sugar and mix those in, breaking up the brown sugar, until everything seems evenly distributed.
Scatter the cup up butter over the dry ingredient and mix it around with the paddle attachment or your hands until the flour is moistened. It should be clumpy and dry, but hold together when you press it.
In a second bowl, beat together the egg, water and vanilla. Pour the egg mixture into the flour mixture and using the paddle attachment (or a big spoon), mix it around until you have a not-too-sticky dough. If it’s very dry, you’ve probably used too much flour, but the cookies should still be okay. Stir in the chocolate chips.
Using a standard size ice cream scoop or a 1/3 cup measure (slightly heaping), spoon up about 8 or 9 giant rounds of dough. Arrange them on a plate and chill overnight or for as many hours as you can stand to wait.
Preheat oven to 400 degrees F. Set a baking sheet on top of a jelly roll pan. Lay a piece of parchment paper over the cookie sheet. Place 5 balls of dough on the cookie sheet (or start with one so that you can determine the correct baking time) and put the sheet in the oven. Immediately reduce heat to 350 F and bake the cookies for a total of 18-20 minutes, checking at 15.