1/4 to 1/3cuppacked brown sugar(certainly use 1/4 cup if you add a caramel sauce)
1/4cupbutter(cold and cut into cubes)
caramel sauce for toppingoptional
Heat oven to 300F. Line the bottom of an 8x8 inch pan with parchment paper if you plan to remove the bars from the pan to cut them. Otherwise, grease the pan.
Combine melted butter, sugar, vanilla, salt, and flour, stirring until just combined. Press mixture evenly into bottom of the pan. Bake for 15 minutes. Meanwhile, prepare apples and streusel.
Toss sliced apples with flour, sugar, cinnamon, and nutmeg until apples are evenly coated. Set aside.
Stir together oats, brown sugar, flour, and cinnamon. Use a pastry cutter (or two knives) to cut the cold, cubed butter into the mixture. The mixture will be be a soft, crumbly cookie dough once you're done.
After removing the crust from the oven, turn the temperature up to 350F. Spread apples evenly on the shortbread, patting them down. Sprinkle streusel on top of the apple layer. Bake 30-35 minutes, until streusel is golden brown.
Cool completely before cutting. If using parchment, lift the parchment out of the pan, and cut into bars. (I like using a bench scraper to cut bar cookies like this.) Store in the refrigerator.
Apple Pie Bars https://foodsilike.net/apple-pie-bars/