Preheat the oven to 350F. Use the butter to grease an 8x8" baking dish, or a 9" loaf tin.
Combine the maple syrup, salt, milk, egg, and vanilla. Use a whisk to mix until the egg is totally combined and the mixture is smooth.
In a separate bowl, mix together the oats and cinnamon. Once mixed, add to the wet mixture and stir to combine. Fold in ⅔ of the chopped apple, and half of the peanut butter.
Pour into the prepared dish, and drop the remaining peanut butter on top, along with the remaining apples. Bake for 45-50 minutes. The mixture should be set and beginning to turn golden on top.
Serve with half & half or more peanut butter.
Recipe by The Kitchen Paper at http://c02.ddd.mwp.accessdomain.com/apple-peanut-butter-baked-oatmeal/