Preheat the oven and prepare the pan: Set your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper for easy removal.

Make the crust: In a bowl, mix 1 cup graham cracker crumbs and 1/4 cup granulated sugar. Stir in 1/2 cup melted unsalted butter until the mixture is crumbly and holds together when pressed.

Press and bake crust: Press the crust firmly into the bottom of the prepared pan. Bake for 8-10 minutes until lightly golden. Let the crust cool completely.

Prepare the cream cheese layer: Beat 8 oz softened cream cheese until smooth. Gradually add 1/2 cup powdered sugar and continue beating until fluffy. Gently fold in 1 cup whipped topping using a figure-eight motion.

Spread the cream cheese layer: Evenly spread this creamy mixture over the cooled crust. Place the pan in the refrigerator while preparing the lemon filling.

Make lemon filling: In a separate bowl, whisk together 1 (14 oz) can sweetened condensed milk, 1/2 cup fresh lemon juice, zest of 1 lemon, and 4 large egg yolks until smooth.

Assemble and bake: Pour the lemon mixture over the cream cheese layer and spread evenly. Bake at 350°F for 15-20 minutes, or until the lemon filling is set but slightly jiggly.

Cool and chill: Remove the bars from the oven and let them cool to room temperature. Refrigerate for at least 4 hours, preferably overnight, to allow flavors to meld and the layers to firm.

Optional topping: Whip 1 cup heavy cream with 2 tablespoons powdered sugar and 1 teaspoon vanilla extract until stiff peaks form. Spread over chilled bars before serving.

Cut and serve: Use the parchment to lift bars out of the pan. Cut into 9 to 16 squares, wiping the knife with hot water between cuts for clean edges. Garnish with extra whipped cream, lemon slices, and powdered sugar if desired.