Grease and line the base of a 20cm round tin with parchment paper.
Make the crumble topping first: in a bowl, rub the butter, flour, salt and sugar together into fine crumbs. Add the desiccated coconut and stir. Set aside.
For the cake, sift the flour, baking powder, salt and cinnamon into a large bowl. Top and tail the blackcurrants. Set aside.
In another large bowl, using an electric whisk, or in a free standing food mixer, beat the sugar, cooled melted butter, eggs and vanilla extract until thick and creamy; this will take a few minutes on high speed.
With a large spoon, fold in the flour mixture, alternating with the yogurt. Don't over-mix, otherwise you will deflate the egg mixture.
Pour the batter into the prepared tin, scatter the blackcurrants over the surface (reserve a small handful to scatter on top of the crumble). Gently push them in. Sprinkle over the crumble, top with the reserved blackcurrants and bake in the preheated oven for 45-50 minutes, or until a skewer comes out clean.
Notes
*The addition of baking powder is not a mistake. I find the cake batter needs a little extra boost as it has the weight of the crumble to contend with.