Preheat oven to 350 degrees F and line 2 cookie sheets with unbleached parchment paper. In a large bowl, add butter and sugar, and beat with an electric mixer until creamy. Add egg and vanilla extract, beat until combined.
Add baking soda, salt, flour and beat until cookie dough forms. Add 1/4 cup chocolate chips and stir with a spatula.
Scoop dough with medium cookie scoop (1 oz size) or a heaping tablespoon and roll into balls, and place on prepared baking sheets 2-3 inches apart. Cookies do spread.
Bake for 10-12 minutes and remove while cookies appear underbaked, puffy and light in color. Let cookies cool on a baking sheet for 15 minutes before transferring onto a cooling rack to cool more.
Notes
Store: Store in a container for up to 5 days. Oat flour cookies dry out fast.
Freeze: Bake, cool cookies completely, place in a resealable plastic bag or container and freeze for up to 3 months. Thaw on a counter for a few hours.
*Oat flour: I used Quaker oat flour. You will need 225 grams which for me consistently is 2 cups. Weigh on scales to be sure!!! You can make homemade oat flour by grinding oats in a high-speed blender and not food processor. You must sift it through the fine mesh strainer otherwise cookies will not turn out!
Butter: Softened butter means a dent appears when you touch it with a finger. To soften butter, just leave it at room temperature for 2-3 hours. To speed up softening, cut up in cubes. If you use salted butter, omit salt. I also do not recommend coconut oil because cookies will be cake-y.
Sugar: I recommend white sugar. I tested coconut sugar and cookies were a bit more cakey but you can.