Blend together all-purpose flour, wheat flour, sugar, and salt in a food processor until well combined. Cut in cold butter until the mixture resembles coarse crumbs. Mix in egg yolk and milk till just combined. Press the dough into a pie pan, cover with plastic wrap, and chill for at least 1 hour.

Preheat oven to 400°F (200°C). Toss chopped rhubarb with sugar, vanilla paste, cardamom, and ginger in a mixing bowl. Spread on a baking sheet, cover with foil, and roast for 20 minutes until tender. Uncover and bake for an additional 5-10 minutes until softened and slightly caramelized. Let cool to room temperature.

Preheat oven to 375°F (190°C). Line chilled pie crust with parchment and fill with pie weights or dried beans. Bake for 10-12 minutes, remove weights and parchment, then return to the oven for another 3-5 minutes until lightly golden.

In a mixing bowl, combine sugar, yogurt, eggs, lemon zest, and lemon juice. Whisk until smooth and creamy. Ensure all ingredients are incorporated.

Spread the cooled rhubarb over the baked pie crust. Pour the lemon filling over the rhubarb. Bake in a 375°F (190°C) oven for 20-25 minutes until edges are set.

Remove pie from oven and let cool at room temperature for 2-3 hours before refrigerating for several hours.

Slice the pie into wedges and serve chilled, topped with whipped cream.