Preheat oven to 350 degrees F.

Prepare an 8-inch baking pan by lining it with a large sheet of heavy duty aluminum foil. Spray with non-stick spray.

Combine melted butter, brown sugar, and vanilla in a mixing bowl and whisk until smooth and the sugar has absorbed the butter.

Add flour, oats, baking soda, and salt. Stir with a wooden spoon until thoroughly combined.

Sprinkle half of mixture into prepared baking pan. Press flat with hands.

Bake until set and golden on the edges, about 13 minutes. Remove from oven and let cool for a few minutes.

Toss sliced apples with lemon juice and sugar. Sprinkle on flour and mix to combine.

Layer sliced apples over crust.

Pour caramel sauce over the apples.

Crumble reserved half of dough and sprinkle in small pieces over apples and caramel sauce.

Bake until golden brown around the edges, about 30-35 minutes.

Serve warm with ice cream or cool and cut into squares.

Best when eaten on the day they are baked.