Prepare the Crust: In a food processor, combine all-purpose flour, wheat flour, cardamom, sugar, and salt. Pulse until mixed, then add cold butter, mixing until crumbly. In a bowl, whisk together the egg yolk and milk, and then blend this mixture with the flour mixture until a dough forms. Chill the dough for 1 hour in the refrigerator.

Pre-cook the Rhubarb: Preheat your oven to 350°F (175°C). In a baking dish, toss the chopped fresh rhubarb with sugar and ground cardamom. Cover with foil and bake for 20 minutes, then remove the foil and bake for an additional 5-10 minutes until tender. Allow it to cool while you prepare the crust and filling.

Blind Bake the Crust: Preheat the oven to 375°F (190°C). Roll out the chilled dough on a floured surface to fit a pie pan, transfer it to the pan. Line the crust with parchment paper, fill it with pie weights, and bake for 13-17 minutes until lightly golden. Cool slightly before adding filling.

Blend the Filling: In a blender, combine sugar, yogurt, eggs, lemon zest, and fresh lemon juice. Blend until smooth and creamy. Set the filling aside while you assemble the pie.

Assemble the Pie: Spread the cooled rhubarb evenly across the bottom of the baked pie crust. Pour blended lemon filling over the rhubarb, ensuring it covers all the fruit evenly.

Bake the Pie: Bake at 375°F (190°C) for 20-25 minutes. The filling should be set with a slight jiggle in the center. Keep an eye on it to prevent overbaking.

Cool and Serve: Remove from oven and let it cool at room temperature for 2-3 hours. Refrigerate for at least an hour before slicing. Serve chilled, topped with whipped cream or vanilla ice cream.