Start by lining the bottom of a 9-inch springform pan with parchment paper. Grease the sides with butter. Preheat your oven to 180°C/356°F top and bottom heat, or 160°C/320°F fan/convection. Wash the red currants and remove them from the vine. The best way is to use a fork and pull the vines through the prongs, so the berries fall off.
1 lb red currents
For the cake base, using a hand or stand mixer, whisk the butter until creamy. Add the egg, sugar, vanilla extract, lemon juice, and salt, and mix until combined. Now add the flour, baking powder, and milk, and mix to a rather thick dough.
Pour and spread the dough into the prepared pan. Then sprinkle the breadcrumbs on top. This will help keep the bottom from getting soggy with red currant juice.
2 tbsp breadcrumbs
Prepare a clean mixing bowl, making sure there's no grease left in it (you can wipe it with white vinegar to be sure). Whisk the egg whites and a pinch of salt on high speed until they start to stiffen. Add the sugar bit by bit. Once the egg whites are very stiff, carefully fold in the ground almonds. Don't overmix, or the egg whites will deflate.
Divide the meringue mixture evenly into two portions. Fold the red currants into one portion and spread them over the cake base.
Use the remaining portion to cover the cake completely. Place in the preheated oven on the middle rack. Bake for a total of 80 minutes.
After about 10 minutes you'll see the top starting to brown (see pictures). At this point, cover the cake loosely with a sheet of parchment paper to keep it from getting too dark, and continue baking for the remaining time.
Remove the cake from the oven and let it cool for about 1 hour before slicing. If you like, sprinkle with powdered sugar before serving.