To make the dough, in a large bowl combine the flour, 150 g ground almonds, baking powder, half the sugar, pinch of salt and stir well using a whisk. Add the butter, sour cream, egg, almond extract and stir to combine until the mixture becomes crumbly. Continue mixing the ingredients with your hands until they form a sticky dough ball. Cover with cling film (in the same bowl) and refrigerate for 1 hour.
Grease the bottom of a 23 cm springform pan, cover with parchment paper and close the side.
Preheat the oven to 350 F/ 180 C/ gas mark 4. Divide the dough into 2 parts (⅔ and ⅓). Place the small dough in the freezer (it'll be easier to work with). Flatten the larger dough on top of parchment paper until it is big enough to cover the bottom of your springform pan. Lift the paper with the dough, turn over and let the dough drop into the pan. Press down to ensure it covers the bottom of the pan evenly.
In a large bowl combine the redcurrants, remaining sugar and 2 tablespoons of ground almonds, stir, being careful not to break up the fruit, and tip the mixture quickly onto the dough spreading evenly. Grate or shred the smaller dough over the fruit, sprinkle with the almond flakes and bake for 50 minutes. Remove from the oven, let cool a little and enjoy!
When you've divided the dough into 2 parts place the smaller dough in the freezer (it'll be easier to work with) while you flatten the larger dough and prepare the fruit. Remove from the freezer just before grating it over the cake.
Do NOT prepare the fruit ahead or it will start releasing juices. Combine the fruit with the sugar and ground almonds just before scattering over the cake.
Freeze the cake (unbaked), covered, for up to 3 months. Bake from frozen according to Instructions (for approx. 1 hour).