Heat oven to 350°F. Line an 8-inch square pan with parchment, leaving overhang.
Whisk flour, oats, both sugars, baking powder, cinnamon, and salt in a large bowl.
Stir in melted butter and vanilla until the mixture looks evenly moistened and clumpy.
Press about two-thirds of the crumb mixture firmly into the pan. Bake 10–12 minutes until lightly set.
Toss apples with lemon juice, sugar, cornstarch, cinnamon, nutmeg, salt, and vanilla; set aside.
Make caramel: melt butter with brown sugar in a saucepan over medium heat, stirring until bubbling.
Whisk in cream and simmer 2–3 minutes. Remove from heat; whisk in peanut butter, vanilla, and salt until smooth.
Layer apples evenly over the warm crust. Drizzle about half the peanut butter caramel over the apples.
Crumble the remaining oat mixture on top, leaving some apples peeking through.
Bake 30–35 minutes until the topping is golden and the filling bubbles at the edges.
Cool in the pan for 1 hour. Drizzle with remaining peanut butter caramel, then slice into bars.
Notes
Variation: Sprinkle chopped roasted peanuts on top with the final drizzle for crunch, or add a pinch of flaky salt before serving. Storage: Keep bars covered at room temperature for 1 day, or refrigerate up to 5 days; warm briefly to soften the caramel.This recipe is an original creation inspired by classic Apple Pie Bars with Peanut Butter Caramel flavors. All ingredient ratios and instructions are independently developed.