Enough granulated sugar and cinnamon to roll dough-balls in
You can substitute salted butter for the unsalted; just leave out the salt in the recipe.
The carbonated water stands in for one large egg. Feel free to use another egg substitution if you have one handy.
Toss together the flour, baking soda, cornstarch, cinnamon, and salt in a large bowl. Set aside.
In a medium size bowl, whisk the melted butter and brown sugar together until no brown sugar lumps remain. Whisk in the carbonated water, then whisk in the vanilla.
Pour the wet ingredients (sugar counts as a "wet ingredient") into the dry ingredients and mix together with a large spoon or rubber spatula. Cover the dough and chill for at least 2 hours, or up to 3 days.
Take the dough out of the refrigerator. If it chilled for more than 2 hours, allow it to sit at room temperature for 10 minutes to soften slightly.
Preheat the oven to 325F (163C).
Line two large baking sheets with parchment paper or silicone baking mats. (Or use one baking sheet, and set some of the dough aside for another batch.)
Pour the granulated sugar and cinnamon into a bowl and mix together. Roll some dough into a ball. If the dough is crumbly, wet your hands with some water before rolling.
Roll the dough-ball into the cinnamon-sugar mixture and place on the baking sheet. Repeat.
Bake for 8-9 minutes.
Remove from the oven and gently press the top of the cookie down with your fingers, or use a utensil to give it some texture.
Place back into the oven for 1-2 minutes.
It’s okay if the cookies still look a little soft. Remove from the oven and allow to cool on the baking sheet for 10 minutes before transferring to a wire rack to cool completely.