1. Preheat your oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper.

2. In a bowl, mix graham cracker crumbs, melted butter, sugar, and cinnamon. Press the mixture into the bottom of the prepared pan. Bake for 10 minutes, then let cool.

3. Beat cream cheese and sugar until smooth. Add eggs one at a time, mixing well after each. Stir in vanilla extract. Pour over the cooled crust and spread evenly.

4. Toss diced apples with lemon juice, brown sugar, cinnamon, and nutmeg. Spread the apple mixture evenly over the cheesecake layer.

5. In a bowl, mix flour and brown sugar. Cut in cold butter until the mixture is crumbly. Stir in chopped pecans (if using). Sprinkle the streusel over the apple layer.

6. Bake for 45-50 minutes, until the streusel is golden and the cheesecake is set.

7. Allow the bars to cool completely at room temperature, then refrigerate for at least 2 hours.

8. In a saucepan, combine sugar and water over medium heat, stirring until sugar dissolves. Increase heat and cook without stirring until the mixture turns amber (8-10 minutes). Remove from heat and carefully whisk in heavy cream, followed by butter and salt, until smooth. Let cool slightly.

9. Cut the chilled bars into squares and drizzle with warm caramel sauce just before serving.