Preheat oven to 350F. Grease an 8×8 inch pan with cooking spray and set aside. Sift together flour, baking powder, baking soda, cinnamon, and nutmeg into a medium-sized bowl. Set aside.
In another medium-sized bowl, using an electric hand mixer, beat together sugar, oil, and egg until smooth and blended. Add flour mixture and beat until well-combined. Batter will be thick. Fold in diced apples.
Spoon about 2/3 of batter into prepared pan and spread evenly with an offset spatula. In a small saucepan over medium-low heat, melt together caramel candies and heavy cream, stirring constantly so mixture doesn’t burn. Once caramel is completely melted and smooth, drizzle over batter.
Spoon remaining batter in dollops over caramel, then swirl it in gently with a knife. Bake for 25-30 minutes, or until golden brown and a toothpick comes out with a few, moist crumbs attached. Cool in pan on wire rack for 20 minutes before cutting into squares and serving.