3 1/3 cups of all purpose flour (400 g)
slightly more than 1 1/3 cup icing sugar (140 g)
1 cup butter (240 g)
4 egg whites
almost 1 ¼ cup milled walnuts (180 g)
2 cups icing sugar (200 g)
Mix all the ingredients and make the dough, let it mature in the cold.
Line baking sheet with parchment paper and roll out the dough. For perfection, you can press the dough with your palms and fingers into the corners and edges of the baking tray.
Spread redcurrant jam on the dough. The jam layer can be quite thick (your preference).
Whisk the egg whites to a soft peak stage. Mix the whites carefully with icing sugar first and then add the milled walnuts. Spread the egg whites mixture over the jam layer and smooth out the top.
Bake carefully in a preheated oven until pink, about 20 minutes at 320-338 °F (160-170 °C). Check the bake by carefully sticking a skewer into the edge of the dough. If your skewer comes out clean, the London bars are done. While still hot, cut the pastry into squares or rectangles.
Good advice: if you are baking London bars for the first time, double the recipe. Why? You will know it when you taste them.