Preheat the oven to 350°F (175°C) and grease a 9x13-inch baking dish. In a large bowl, mix the flour, sugar, and salt. Cut in the butter with a pastry cutter or hands until a crumbly texture forms. Press half of this mixture into the baking dish and bake for 15 minutes until lightly golden.

In a medium saucepan over medium heat, combine apples, brown sugar, cinnamon, cornstarch, vanilla extract, and lemon juice. Stir and cook for about 5 minutes, until the apples soften and the mixture thickens slightly.

Spread the apple filling evenly over the pre-baked crust. Sprinkle the remaining crumb mixture on top, ensuring an even layer over the apples.

Return the dish to the oven and bake for 30 minutes or until the top is golden brown. Let the bars cool completely before slicing to ensure they set properly.

Once cooled, cut into squares and serve. These bars taste great as is or topped with a scoop of ice cream or caramel drizzle!