Preheat the oven to 350 degrees.
In a medium bowl, whisk together the brown sugar, salt, cinnamon and corn starch. Add the sliced apples and mix until fully coated.
In a separate bowl, mix together the flour, oats, brown sugar, cinnamon and salt.
Place a 10-inch cast iron skillet or another deep, oven safe skillet over medium-high heat. Add the butter and let it melt until it begins to foam. Swirl the melted butter around the pan and keep a close eye on it until it starts to turn golden brown and smell nutty. Be careful not to let the butter burn.
Remove it from the heat and immediately pour the browned butter into the flour mixture, being sure to scrape in all of the browned bits from the bottom of the pan.
Mix together until the butter is fully incorporated and starts to form clumps. Sprinkle over the apples and spread it out until evenly coated.
Bake for about 30 minutes, or until the top has nicely browned and the filling is bubbling. Serve warm, preferably with vanilla ice cream.