1 cup (2 sticks) unsalted butter, super soft
2/3 cup packed light brown sugar
1/3 cup sugar
2 teaspoons vanilla extract
1 cup flour OR 1/2 cup cornstarch OR 1 1/3 cup oat flour
3 cups rolled oats
1 teaspoons salt
1/4 teaspoon baking soda
1/8 teaspoon baking powder
STEP 1 Heat the oven to 350°f.
STEP 2 Combine the butter and sugars in a large mixing bowl, smoothing together with some muscle. Add in egg, and mix to combine.
STEP 3 Add the oats - if you are using instant oats, stop here and set aside. If using rolled oats add in flour (or oat flour, or cornstarch), baking powder, baking soda, and salt. Mix until your dough comes together and any remnants of dry ingredients have been incorporated. The dough will be a slightly fluffy, fatty mixture in comparison to your average cookie dough. Scrape down the sides of the bowl.
STEP 4 Pam-spray a pan (8x8 or 9x13). Pour your dough into your pan and push lightly to fill the pan.
Swirl in 1/2 cup or your fave filling - think jam, nutela, jam, honey - use a knife to twirl it in between the whole pan of dough, making ribbons of filling.
STEP 5 Bake for 20-30 minutes depending on the size of your pan.
Wrapped well in plastic, the oat cookie will keep fresh in the fridge for up to 1 week.