How to Make It
Preheat oven to 350ºF. Line a 9-by-13-inch baking pan with heavy-duty foil, leaving an overhang at both short ends; mist with cooking spray.
Make crust and topping: Using an electric mixer on medium-high speed, beat butter and sugar until light, about 3 minutes. Scrape down sides of bowl and beaters. Reduce mixer speed to low and mix in flour, cinnamon and salt. Remove 3 1/2 cups of dough; press evenly into baking pan. Bake until lightly browned around edges, about 20 minutes. Let cool completely on a wire rack. Mix oats into remaining dough for topping; cover and refrigerate.
Make filling: Melt butter with brown sugar in a large skillet over medium-low heat, stirring until sugar has dissolved. Add apples and cinnamon; stir to coat. Cover and cook until softened, about 15 minutes, stirring occasionally. Remove lid, raise heat to medium-high and cook until all liquid has evaporated, about 3 minutes, stirring occasionally to prevent apples from sticking. Remove from heat. Let cool slightly.
Assemble bars: Raise oven temperature to 400ºF. Spread apples evenly over crust. Scatter crumble topping over apples. Press down lightly. Sprinkle with raw sugar and bake until browned and crunchy on top, 20 to 25 minutes. Let cool completely in pan on wire rack. Lift out of pan using foil overhang. Peel off foil. Cut into 24 bars.