1. Prepare the Shortbread Base:

1. Preheat your oven to 350°F (175°C) and line an 8×8-inch baking pan with parchment paper.
2. In a large bowl, whisk together the flour, powdered sugar, and salt.
3. Add the cold, cubed butter to the dry ingredients. Use a pastry cutter or your fingers to combine until the mixture resembles coarse crumbs.
4. Press the mixture firmly into the prepared pan, creating an even layer.
5. Bake for 20–25 minutes, or until the edges are lightly golden. Let it cool slightly while preparing the filling.

2. Prepare the Lemon Filling:

1. In a medium bowl, whisk together the granulated sugar and eggs until smooth.
2. Gradually add the lemon juice and zest, mixing well.
3. Gently fold in the flour until the mixture is fully incorporated.

3. Assemble and Add the Crumb Topping:

1. Pour the lemon filling over the cooled shortbread base, spreading it evenly.
2. In a separate bowl, mix together the flour, granulated sugar, and melted butter for the crumb topping. Stir until it forms a crumbly texture.
3. Sprinkle the crumb topping evenly over the lemon filling.

4. Bake the Lemon Crumb Bars:

1. Return the pan to the oven and bake for 25–30 minutes, or until the topping is golden brown and the filling is set.
2. Remove from the oven and let the bars cool completely in the pan.

5. Prepare the Glaze:

1. In a small bowl, whisk together the powdered sugar and lemon juice until smooth. Adjust the consistency by adding more lemon juice if necessary.
2. Drizzle the glaze over the cooled bars.

6. Serve and Enjoy:

1. Once the glaze has set, slice the bars into squares or rectangles.
2. Serve chilled or at room temperature.