Preheat oven to 350° F. Line an 8x8 glass dish with parchment paper and lightly spray with nonstick cooking spray. Set aside.
Make the cookie crust. In a large mixing bowl, combine the softened butter, sugar, flour, and vanilla until a soft dough forms. Press the dough evenly into the bottom of the prepared baking dish.
Make the lemon filling. Add the beaten egg, lemon zest, and lemon juice to the cream cheese mixture. Mix for 20–30 seconds, or until the filling begins to thicken. Scrape down the sides of the bowl and mix briefly again until combined.
Assemble. Pour the cream cheese filling evenly over the cookie crust and smooth the top.
Bake for 25–30 minutes, or until the edges are set and the center is just slightly jiggly. Let cool completely, then refrigerate until thoroughly chilled before cutting into squares.
Torch.Sprinkle about 1 teaspoon of fine granulated sugar evenly over each bar. Use a kitchen torch to caramelize the sugar until melted and golden amber.
Chill and cut. Once fully chilled, remove from the refrigerator and cut into 16 squares.
Serve or store. Serve immediately or return the bars to the refrigerator until ready to serve.