Preheat oven to 325° Fahrenheit and line a 8x8-inch baking pan with parchment paper, then lightly grease the inside.
Make the crust by mixing together the graham cracker or cookie crumbs and melted butter or coconut oil in a bowl, then press the mixture into the bottom of your prepared baking pan. Bake the crust for 10 minutes.
While the crust bakes, make the filling by adding all filling ingredients to a blender and blend until smooth. Pour the filling over the crust, then bake for 25-30 minutes or until the bars are just set in the middle. (See Notes below on how to bake in a water bath to avoid any cracks).
Remove the bars from the oven and leave them to cool at room temperature for 1 hour, then transfer them in the fridge to chill for at least 3 hours (or overnight).
Once the bars have chilled, remove them from the pan and cut into squares. Enjoy the lemon bars right away, or store them in an airtight container in the fridge for up to 5 days!