1. Preheat the oven and prepare the pan
Preheat your oven to 350°F (175°C). Line a 9×9 inch baking pan with parchment paper, leaving some overhang on the sides for easy removal later. Lining the pan ensures the bars come out cleanly, and the overhang acts like handles to lift the bars from the pan after they cool.

2. Make the crust
In a large bowl, whisk together flour, granulated sugar, light brown sugar, salt, and baking powder. Pour in the melted and cooled butter and mix until the mixture becomes crumbly but holds together when pressed.
Set aside 1/3 of the mixture for the topping. Press the remaining 2/3 of the mixture into the prepared pan to form an even layer. Bake for 15 minutes, or until lightly golden.

3. Prepare the lemon filling
In another large bowl, whisk together the sweetened condensed milk, egg yolks, heavy cream, and salt until smooth. Gradually whisk in the fresh lemon juice, ensuring the mixture remains smooth and creamy.

4. Assemble the bars
Once the crust has finished baking, pour the lemon filling evenly over the warm crust. Gently sprinkle the reserved crumb mixture over the lemon filling, making sure not to press it down. This crumbly topping will become golden and crisp as it bakes.

5. Bake the bars
Bake the assembled bars for 15-20 minutes, or until the crumb topping is golden and the lemon filling is set but still slightly jiggly in the center. Avoid overbaking, as this can make the filling too firm.

6. Cool and refrigerate
Allow the bars to cool completely at room temperature, then refrigerate for at least 4 hours or overnight. Refrigeration helps the filling fully set and makes the bars easier to slice cleanly.

7. Slice and serve
Once the bars have chilled, use the parchment overhang to lift them from the pan. Cut into squares and serve chilled or at room temperature. For a special touch, serve with a dollop of whipped cream or garnish with fresh berries.