Grease a shallow 24-cm tart pan with removable bottom with butter and line the base with parchment paper.
If using whole raw almonds, first grind them, in a food processor with 1 tablespoon of the sugar until fine. Otherwise, using a food processor, combine the almond meal, butter and sugar and pulse until fully incorporated. Add the egg, buttermilk, orange zest and vanilla and pulse again until well incorporated.
In a medium bowl, whisk together the flour, baking powder, and salt. Add the almond-butter mixture to the bowl with the flour, and using a spatula, stir until just combined. NOTE: Do not over mix!
Scrape the batter into the prepared pan and smooth out the surface with the spatula. Lightly press the rhubarb into the batter and place in the fridge to chill for 30 minutes.
Meanwhile, preheat the oven to 350°F / 175°C (155°C fan-assisted).
Remove the cake from the fridge and lightly sprinkle the turbinado sugar over the batter (if using). Transfer to the preheated oven and bake until the edges are deeply golden brown and a toothpick inserted in the center comes out clean, about 40-45 minutes.
Transfer to a wire rack to cool for 5-10 minutes before slicing and serving. Enjoy!
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Rhubarb Cake with Almonds & Buttermilk - https://ellerepublic.de/en/rhubarb-cake-with-almonds/