Pistachio Lemon Bars

Method

1. 1Make the pistachio shortbread crust. Toast the pistachios in a dry pan over medium heat for 3 to 4 minutes, shaking occasionally, until fragrant and barely darker. Let them cool completely — hot nuts will melt the butter and produce a greasy dough. Preheat the oven to 175°C (350°F). Line a 23 cm (9-inch) square baking tin with two strips of parchment paper going in opposite directions, with overhang on all sides — this makes lifting the bars out later easy. In a food processor, pulse the cooled pistachios with the icing sugar until they're finely ground — stop before they turn into a paste. Add the 150 g of flour, salt, and cardamom and pulse to combine. Add the cold butter pieces and pulse until the mixture looks like damp sand and clumps when you press it between your fingers. Do not over-process. Tip the mixture into the lined tin and press it firmly and evenly into the base — the flat bottom of a measuring cup or glass works well for getting the surface even.
2. 2Blind bake the crust. Bake the crust at 175°C for 18 to 22 minutes until it is pale golden at the edges and feels dry and just set in the center. It won't be deeply browned — that's fine, it will continue cooking when the filling goes in. While the crust bakes, make the filling so it's ready to pour on as soon as the crust comes out.
3. 3Make the lemon filling. In a large bowl, whisk the eggs and caster sugar together vigorously for 1 minute until pale and well combined. Whisk in the lemon juice and lemon zest. Finally, add the remaining 30 g of flour and whisk until completely smooth — no lumps. The filling will be liquid and quite runny; this is correct. Do not use a blender or food processor for the filling — over-mixing creates bubbles that will bake to a pitted surface.
4. 4Bake the bars. As soon as the crust comes out of the oven, pour the lemon filling directly over the hot crust. Scatter the roughly chopped pistachios evenly over the surface of the filling. Immediately return to the oven and bake for 20 to 25 minutes, until the filling is just set — it should have a very slight wobble in the very center when you gently shake the tin, but the edges should be firm and the surface should no longer look liquid or shiny-wet. It will set more as it cools.
5. 5Cool, chill, cut and serve. Allow the bars to cool completely in the tin at room temperature, then refrigerate for at least 2 hours — ideally overnight. Cold bars cut cleanly. Use the parchment overhang to lift the slab out of the tin and place on a cutting board. Dust generously with icing sugar just before serving (dusting too early causes the sugar to dissolve into the surface). Cut into 16 squares with a large, sharp knife, wiping the blade clean between cuts for neat edges. Store covered in the refrigerator for up to 4 days.