Preheat oven to 350 degrees
Line 8" x 8" pan with parchment paper, leaving ends sticking up to use later as handle. Lightly spray with oil.
Mix together all ingredients and pour into greased pan. Press mixture into pan until even thickness
Bake for 20 minutes
Remove pan from oven and reset oven temperature to 275 degrees
Using the parchment paper, remove treats from pan. Cut treats into 1/4" cubes (a pizza cutter works well for this). Return cut treats to pan, spreading out so they're in a single layer.
Bake at 275 degrees for 40-60 minutes until dry all the way through.
You can cut into even smaller treats after second baking. Store in refrigerator.