Let’s break down the process into easy-to-follow steps.

1. Make the Crust:

• Preheat the oven to 350°F (175°C). Grease a 13-by-9-inch pan with butter. (Use an 8-by-10-inch pan if you’d like the layers to be a little thicker.)
• In a large bowl, stir together the flour, sugar, and salt.
• Add the cold, cubed butter and use a pastry cutter (or your fingers) to cut it into the flour mixture until it resembles fine crumbs.
• Press the mixture into the prepared pan.
• Bake until golden around the edges, about 20 minutes.

2. Make the Filling:

• In a medium bowl, stir together the sugar and flour.
• Crack in the eggs, and whisk to combine.
• Add the lemon zest and juice, and mix until combined.

3. Assemble and Bake:

• Pour the lemon filling over the hot, pre-baked crust.
• Return the pan to the oven and bake until the filling is set, about 20 minutes.

4. Cool and Finish:

• Allow to cool in the fridge for a minimum of 2 hours.
• Sift powdered sugar over the top before cutting into squares.

These steps are easy to follow.