Preheat to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with a piece of parchment paper.
In a small bowl, combine flour, sugar, salt, and chopped almonds. Add cold butter cubes and mix until crumbly, using your fingers or a fork. Chill until needed.
In a large bowl (or the bowl of a stand mixer), whisk yogurt, eggs, sugar, oil, and vanilla until smooth (you can optionally add lemon zest).
Sift in flour, baking powder, and salt. Stir gently until just combined. Fold in red currants.
Pour the cake batter into the prepared cake pan and smooth the top. Add a layer of red currant berries on top of the cake. Sprinkle the crumble evenly over the surface — don’t press it in.
Transfer the cake into the preheated oven and bake for 35–40 minutes, or until the top is golden brown and a toothpick inserted in the center of the cake comes out clean or with moist crumbs. If the crumble browns too fast, tent loosely with foil for the last 10 minutes.
Let cool in the pan for 15–20 minutes, then run a knife around the edges and carefully remove. Cool completely on a wire rack. Dust with powdered sugar or add a lemon glaze if desired.
Notes
Use room temperature ingredients – Yogurt, eggs, and oil mix more smoothly and help create an even crumb.Don’t overmix the batter – stir just until the flour disappears to keep the cake tender. Chill your crumble topping – it keeps the butter firm, so the topping bakes up crisp and golden.