Place oats in a blender or food processor and blend until fairly oats break down to a flour-like consistency. Measure out 2 cups of blended oats.
Mix blended oats with baking soda and set aside.
Cream peanut butter, butter and sugars together until smooth. Add in egg and vanilla, beating until smooth.
Stir in oat mixture. Add in chocolate chips and mix until just combined.
In a 9 inch springform pan, or pizza pan, spread out dough evenly, leaving a 1/2 inch border around edges of pan.
Bake for 18-20 minutes until center is set.
Allow to cool in the pan for 10 minutes on a cooling rack. Remove sides of springform pan and then let cool completely before icing.
Beat together the butter and peanut butter and add in powdered sugar slowly.Be sure your powdered sugar is sifted to prevent clumps in your icing. Add 1 tablespoon of milk at a time, to thin icing to desired consistency.
Pipe out frosting along edges and/or to spell out Happy Birthday.
Be sure to use certified gluten-free oats. Quick cooking oats or regular old fashioned oats both work well to be blended into oat flour.
The oats are to be measured AFTER blending in this recipe for Chocolate Chip Peanut Butter Cookie Cake.
If you don't like peanut butter or have an allergy, feel free to sub it out for almond butter.
This cookie cake will last for 3 days at room temperature.