Preheat oven to 325 degrees F.
Line 2 baking sheets with parchment or a silpat baking sheet.
In a medium bowl, whisk the cake flour, baking powder, baking soda and salt.
3 cups cake flour, 1 teaspoon baking powder, 1/2 teaspoon baking soda, 1/4 teaspoon salt
With an electric mixer, mix the sugar, butter and sour cream until light and fluffy.
1 cup granulated sugar, 8 Tablespoons butter, 1/2 cup sour cream
Add the vanilla and egg and mix until combined. Add the flour mixture, one cup at a time, and mix until combined. Don’t overmix.
2 teaspoons vanilla, 1 egg
Using a medium-sized cookie or ice cream scoop, drop level scoopfuls of dough onto the prepared baking sheets. Space cookies out to leave room for them to spread.
Dip the bottom of a glass into some flour and gently press the cup on top of each cookie to flatten to desired height. Cookies should be about 1-½ inch circle before baking. If the sides split while you press, smooth them out with your finger before baking.
Bake for 20 minutes or until the cookies rise and are just starting to get golden brown on the bottom. Remove from oven and let cool on the baking sheets for 1-2 minutes. They will continue to cook while on the hot cookie sheet. Place cookies on a wire rack to cool completely.