Preheat the oven to 180C/350F/Gas 4. Line a 9x13-inch baking tray with foil and grease with baking spray or butter. Set aside.
Using a handheld or stand mixer, beat together the butter, flour, sugar, and salt until a crumbly dough forms. Press the mixture into the prepared baking tray, and bake for 15 - 20 minutes until lightly golden.
For the filling
Whisk together the eggs, lemon juice, zest, sugar, and flour. Pour over the hot baked crust, and bake for an additional 30 - 35 minutes until the filling is set.
Allow to cool completely in the pan on a wire rack. Dust with icing sugar, then slice and serve.
I like to refrigerate my bars for a few hours or overnight for neater slices.
Notes
Lemon bars can be kept in an airtight container at room temperature or in the fridge for up to 3 days. They also freeze well for up to 1 month. Thaw overnight in the fridge before serving.You can half this recipe to bake in an 8x8-inch square pan.