Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper or spray with baking spray.
Combine flour, brown sugar, and salt in a medium bowl. Use a pastry cutter to cut in the butter until the mixture resembles coarse crumbs. Press into the prepared 9x13-inch pan. Bake for 10 to 15 minutes or until lightly browned just around the edges.
2 cups (282g) all-purpose flour, ½ cup brown sugar, ¼ teaspoon salt, 1 cup (227g) salted butter
Beat cream cheese and sugar in a large bowl with an electric mixer until smooth. Add eggs, one at a time, and vanilla extract, mixing on low speed and stopping to scrape the bottom and sides of the bowl. Pour over the warm shortbread crust and spread into an even layer.
2 (8-ounce) packages cream cheese, ½ cup (100g) granulated sugar, 2 large eggs, 1 teaspoons pure vanilla extract
Stir together the chopped apples, sugar, cinnamon, and nutmeg in another bowl. Spoon over the cheesecake layer.
3 Granny Smith apples, 2 Tablespoons granulated sugar, ½ teaspoon ground cinnamon, ¼ teaspoon ground nutmeg
Combine the flour, brown sugar, and cinnamon in a medium bowl. Use a pastry cutter to cut in the butter. Sprinkle the streusel topping over the apple filling.
1 ½ cups (212g) all-purpose flour, ½ teaspoon ground cinnamon, ½ cup (113g) salted butter, 1 cup (200g) brown sugar
Bake for 40 to 45 minutes or just until the filling is set. Cool for 2-3 hours at room temperature before transferring to the fridge to chill for 4 hours or overnight.
Combine the butter, sugar, cream, and salt in a medium saucepan over medium-low heat. Bring to a simmer and cook for 5-7 minutes while stirring almost constantly until thickened slightly. Stir in vanilla extract, then remove from heat and cool before drizzling over the finished bars. This can be made ahead and refrigerated until ready to use. Reheat in a microwave until runny enough to pour before using.
4 Tablespoons salted butter, 1 cup (200g) granulated sugar, ½ cup heavy cream, Pinch of salt, 2 teaspoons pure vanilla extract
Cut into bars then drizzle with caramel sauce before serving.