Preheat oven to 350 degrees and prepare a large baking sheet with parchment paper.

In a food processor, combine the buckwheat, oats, almond flour, salt, poppy seeds, lemon zest, cardamom, and brown sugar. Pulse to combine, then add in the butter and vanilla. Pulse until the butter is finely ground and the mix is homogeneous. When you squeeze the dough, it should come together and hold its shape, but remain dry and crumbly.

Spread onto the prepared sheet and bake in the oven for 13-15 minutes—until the crumble is lightly golden brown, but not baked fully.

To make the filing, begin by combining half the rhubarb with the strawberries, lemon juice, and brown sugar; mix and set aside.

In a medium saucepan, add wine, sugar, lemon juice, and rhubarb; stir to combine and cook over medium-low heat for 5-6 minutes. While it reduces, combine corn starch and equal parts water to make a slurry.

When the rhubarb has softened, add vanilla and the corn starch slurry, stirring until smooth and thick—about 3 more minutes.

Remove from heat and combine with the remaining strawberries and rhubarb. Stir to combine, then transfer to a square baking dish.

Spread the almond flour crumble on top, then return to the oven for 23-25 minutes, or until the top is golden and the filling is bubbling. Serve with creme fraiche, whipped cream, or ice cream.