Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, letting it hang over the edges by about 2 inches on each side for easy removal.

Mix graham cracker crumbs, melted butter, 1/4 cup granulated sugar, and 1/4 teaspoon cinnamon in a bowl until it resembles wet sand. Press the mixture firmly into the bottom of the prepared pan using the bottom of a measuring cup to pack it to about 1/4-inch thickness.

Bake the crust for 10 minutes, then remove from oven and let cool for at least 5 minutes while preparing the other layers.

Beat softened cream cheese and 1/2 cup granulated sugar with an electric mixer on medium speed for 2-3 minutes until completely smooth and fluffy. Add eggs one at a time, mixing on low speed after each addition just until combined. Stir in vanilla extract.

Pour the cheesecake mixture over the cooled crust and spread evenly with a spatula.

In a separate bowl, toss diced apples (cut into 1/2-inch cubes) with lemon juice, 1/4 cup brown sugar, 1 teaspoon cinnamon, and nutmeg. Spread the apple mixture evenly over the cheesecake layer.

In a clean bowl, mix flour and 1/4 cup brown sugar. Cut in cold butter cubes using a fork or pastry cutter until the mixture forms pea-sized crumbles that resemble coarse sand. Stir in chopped pecans if using.

Sprinkle the streusel topping evenly over the apple layer.

Bake for 45-50 minutes, until the streusel turns golden brown (the color of peanut butter) and the cheesecake layer is set with only a slight jiggle in the very center when gently shaken. Allow to cool completely at room temperature for 1-2 hours.

Refrigerate the cooled bars for at least 2 hours or overnight before cutting.

For the caramel sauce, combine 1 cup granulated sugar and water in a heavy-bottomed saucepan over medium heat, stirring until sugar dissolves completely. Increase heat to medium-high and cook without stirring, swirling the pan occasionally, until the mixture turns deep amber (the color of an old penny), about 8-10 minutes. Watch carefully as it can burn quickly.

Remove caramel from heat and carefully whisk in heavy cream at arm's length as it will bubble vigorously and release hot steam. Stir in 2 tablespoons butter and salt until smooth. Let cool for 5-10 minutes until it thickens slightly.

Using the parchment overhang, lift the bars from the pan. Cut into 24 squares using a sharp knife, wiping the blade clean between cuts. Let bars sit at room temperature for 15 minutes, then drizzle with warm caramel sauce just before serving.