Combine flour, baking powder, 100g caster sugar, butter and egg yolks in a large bowl. Knead together with your hands till well combined. Wrap in cling film and chill in the fridge for 30 minutes.
Preheat the oven to 200 C / Gas 6. Grease a 26cm springform cake tin.
Roll out the chilled dough on a floured surface to roughly the same diameter as the tin. Transfer to the tin and press to even out along the bottom and a little up the sides.
Beat egg whites to stiff peaks. Gradually beat in 150g sugar. Add the ground hazelnuts and two handfuls of redcurrants, then gently mix together with a spoon.
Place the remaining redcurrants over the prepared base in the tin. Cover with the meringue.
Transfer to the bottom shelf of the preheated oven and bake for 50 minutes. Once cooled, run a knife along the edges, remove the sides of the tin and enjoy!