Warm the milk to around 35°C (95°F) - it should feel lukewarm to the touch, not hot, as excessive heat will kill the yeast. Mix the yeast and sugar into the warm milk, then set aside for 10 minutes until you see small bubbles forming on the surface, indicating the yeast is active.
102 ml milk, 7 g instant yeast, 20 g sugar
In a large mixing bowl, combine the flour, egg yolk, salt, and ground hazelnuts. Add the foamy milk mixture and softened butter. Using a stand mixer with dough hook attachment (or knead by hand), mix until the dough comes together and becomes smooth and elastic, about 5-7 minutes.
200 g flour, 1 egg yolk, 1 pinch of salt, 20 g butter, 35 g ground hazelnuts
Cover the bowl with a damp cloth or plastic wrap and let the dough rise in a warm place for at least 30 minutes until slightly puffed.
Prepare the Red Currant Topping
In the meantime, prepare the red currant topping. Mix the butter, confectioners/ icing sugar and vanilla sugar (or extract) until it starts to smooth cream.
75 g butter, 30 g icing / confectioners sugar, 1 teaspoon vanilla sugar
Wash the red currants and remove them from their stems using a fork - simply run the fork down each stem to easily strip off the berries.
250 g red currants
Assemble and Bake
Preheat your oven to 160°C (320°F) with fan setting. Grease a 27cm (10-inch) tart or shallow pie dish with butter, then sprinkle with breadcrumbs to prevent sticking.
2 tablespoon breadcrumbs
Roll out the risen dough to fit your dish, making it about 3-4mm thick and ensuring you have enough to cover the edges. Transfer the dough to the prepared dish and let it rest for another 10 minutes.
Using your fingertips, create small indentations all over the dough surface. Fill these dimples with the vanilla butter mixture using a spoon or piping bag for precision. Evenly distribute the red currants over the entire surface.
Bake for 30-35 minutes until the dough is golden brown and cooked through. Test doneness by inserting a skewer into the cake - it should come out clean.
Allow the cake to cool slightly before serving. Enjoy warm or at room temperature.