Preheat your oven to 350 degrees. Press tinfoil or parchment paper into a 9inch square pan. Spray lightly with nonstick spray.
Crush your graham crackers using your food processor till a fine crumb is formed.
Combine your graham cracker crumbs, sugar, and butter in a small bowl.
Bake in preheated oven for 5 minutes.
Allow to cool, while preparing filling.
Beat your cream cheese until smooth, for about 1 minute.
Add in your egg, flour, lemon juice, lemon zest and sugar. (Add 1 to 2 drops of yellow food coloring if you want yellow colored bars)
Mix for 2-3 minutes until mixture is completely smooth.
Pour mixture over crust and bake in oven for 25 minutes until the middle is no longer jiggly.
Allow to set at room temperature for 30 minutes. Cover and place in fridge for 3 hours, or overnight before slicing and serving.