For the dough: Put the flour, baking soda, and salt into a bowl and stir it with a whisk to combine. Set aside. Using a hand or stand mixer, beat the butter until it is lighter in color. Slowly add in sugars and beat until it 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 using the low speed, then stir in the chocolate chips. Set aside.
To form the cookies: Use 2 teaspoons of the dough and roll it into balls. Put the balls onto a cookie sheet. When they are all made, 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 half the seltzer and whisk well to combine. Add more seltzer as needed until the batter is thick and the consistency of heavy cream.
To make the cookies: Heat the oil in a deep-fat fryer to 350 degrees F.
Dip the chilled dough balls in the batter and carefully place them into the hot oil. Fry a few at a time, turning them over from time to time, until they are golden brown, about 3 minutes total. Drain on paper towels and serve while still warm.