For the cookie dough: In a large bowl, whisk together the flour, baking soda, and salt. In a standing mixer, cream the butter until it is lighter in color. Slowly add in the sugars and cream it until the mixture is light and fluffy. Add the eggs 1 at a time and beat until they are incorporated. Stir in the vanilla. Add the flour mixture on low speed, and then mix in the chocolate chips.
Take 2 teaspoons of the dough and roll it into balls. Put the balls onto a cookie sheet and put them into the freezer for about 30 minutes to firm up.
For the batter: In a large bowl, whisk together the flour, sugar, and baking powder. Add the egg and the seltzer and whisk well to combine. Add more seltzer, as needed, until the batter is the consistency of heavy cream.
In a large, heavy bottomed stockpot, heat the oil to 350 degrees F.
Coat the chilled cookie dough balls in the batter and very carefully place them into the hot oil. Fry no more than 3 at a time, since you do not want the temperature of the oil to drop. Using a slotted spoon, turn them over a few times until they are golden brown, about 3 minutes total. Remove from the oil and drain on paper towels, sprinkle with fleur de sel, and serve warm.