For the sauce: in a saucepan, combine all ingredients except the vanilla. Heat for 8 to 10 minutes, stirring often, then add the vanilla and continue cooking for one minute. Remove from heat and let cool slightly.
Preheat the oven to 375°F and butter an 8-inch square dish.
In a bowl, add the apple slices, cinnamon, and 4 teaspoons of flour.
Transfer to the prepared baking dish.
Pour 1/2 cup of caramel sauce on top.
In a bowl, mix the oats, brown sugar, chopped pecans, 1/4 cup of flour, salt, and butter. Combine with fingers and sprinkle over the caramel layer.
Bake for 30 to 40 minutes.
Let cool for 20 minutes, then serve with the remaining caramel sauce.
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