Creating Creamy Lemon Cheesecake Crumb Bars is a delightful process. Follow these step-by-step instructions to achieve perfect results:

1. Preheat the Oven: Begin by preheating your oven to 325°F (163°C). Grease a 9×13 inch baking pan with cooking spray or line it with parchment paper for easy removal.

2. Prepare the Crust: In a mixing bowl, combine the graham cracker crumbs, granulated sugar, melted butter, and ground cinnamon (if using). Stir until the mixture resembles wet sand.

3. Press the Mixture: Firmly press the crumb mixture into the bottom of the prepared baking pan. Use the back of a measuring cup or your fingers to create an even layer.

4. Bake the Crust: Place the crust in the preheated oven and bake for 10-12 minutes, or until lightly golden. Remove from the oven and let it cool slightly.

5. Make the Cheesecake Filling: In a large mixing bowl, beat the softened cream cheese with an electric mixer until smooth and creamy. Gradually add the granulated sugar, mixing until well combined.

6. Add Eggs: Add the eggs one at a time, mixing well after each addition. Ensure that the mixture is smooth and free of lumps.

7. Incorporate Other Ingredients: Mix in the sour cream, fresh lemon juice, lemon zest, and vanilla extract. Beat until everything is well blended.

8. Pour Filling Over Crust: Carefully pour the cheesecake filling over the pre-baked crust, spreading it evenly with a spatula.

9. Prepare the Crumb Topping: In a separate bowl, combine any remaining crumb mixture from the crust (if you have any left) or make a new batch using the same ingredients. Sprinkle this crumb mixture evenly over the cheesecake filling.

10. Bake the Bars: Return the pan to the oven and bake for an additional 30-35 minutes, or until the cheesecake is set but still slightly jiggly in the center.

11. Cool the Bars: Once baked, remove the bars from the oven and let them cool at room temperature for about 30 minutes. Then, refrigerate for at least 2 hours before cutting into squares.

12. Slice and Serve: Once chilled, use a sharp knife to cut the bars into squares. Wipe the knife between cuts for clean slices.