Preheat the oven to 325F degrees.
Line an 8x8 inch square pan with aluminium foil and grease with non-stick cooking spray.
To make the crust, in a medium bowl stir together the graham cracker crumbs, granulated sugar and melted butter.
Press into the bottom of the prepared pan, and place in the freezer while you make the lemon filling.
To make the lemon layer, in a medium bowl whisk together the lemon juice, lemon zest, egg yolks, sweetened condensed milk and cornstarch. Once evenly combined, whisk in the heavy cream.
Pour the mixture overtop of the crust.
Then bake in your preheated oven for 25-30 minutes. The top should look just set and there can be a little wobble in the middle, but not too much.
Turn off the oven and open the oven door. Then let the cake cool in the oven for about 10 minutes, before removing from the oven and allowing to cool at room temperature.
Once completely cooled, cover and place in the fridge for at least 4 hours.
To serve, cut into bars and top with whipped cream.