Finely chop the walnuts, except for a few for decoration. Mix flour, 50 g diabetic sweetener, salt, fat, 1/2 egg yolk and walnuts to a smooth dough. Cover and let rest in the refrigerator for about 30 minutes. Grease a small tart tin (approx. 26 cm Ø). Roll out the dough on a lightly floured work surface and line the mould with it. Refrigerate for another 30 minutes. Prick the dough several times with a fork. Line with baking paper and peas for blind baking. Pre-bake in a preheated oven at 175 °C (fan oven: 150 °C) for about 15 minutes. Beat eggs, rest of egg yolk and remaining diabetic sweetness until frothy. Stir in grapefruit juice. Whip cream until stiff and fold into the egg mixture. Remove baking paper and peas from the dough and spread cream on top. Bake in a preheated oven at 150 °C (fan oven: 125 °C) for 45-55 minutes. Carefully cover the tart 20 minutes before the end of the baking time. Let the tarte cool down on a cake rack. Cut the grapefruits into slices and spread on the tart with the remaining walnuts
Tip: Bake the dough with 200 g sugar instead of diabetic sweetness. If you like, you can glaze the grapefruit slices with some red cake glaze. Dust the tart with icing sugar
Waiting time approx. 1 hour / 2 1/2 BE