Preheat oven to 375 degrees. In a medium mixing bowl, combine flour, brown sugar, ½ tsp. salt, and 2 Tbsp. sugar (reserve remaining sugar). Pinch 4 Tbsp. butter into flour mixture until it resembles wet sand. ("Pinching" is exactly what it reads as: pinch the butter to make smaller pieces of butter.) Add oats and combine everything by squeezing to make some good clumps. Set aside while you prepare your apples.
Prepare the Apples
Peel and core apples and slice into ¼" pieces. If apples are too large, they won't bake completely, so err on the side of small. In a second medium mixing bowl, toss apples with the remaining sugar, vinegar, cinnamon, and nutmeg.
Fill the Pan
Fill foil pan as full as you can get it. The apples will shrink while baking. Cut remaining 2 Tbsp. butter into pieces and place randomly on top of apples.
Top the Filling
Top apples and butter with oat and flour mixture. Again, pile it on there; it's tasty!
Plate the Dish
Bake for approximately 50-55 minutes or until it is a nice golden brown on top and juices from apples are bubbling up around the edges. You may want to put a baking sheet on the rack below the apple crisp to guard against any juice drippings getting your oven messy!Remove from oven, and let cool about 20 minutes before diving in!