Prepare the lievitino: In a bowl, pour the milk, flour, cold butter, and fresh brewer's yeast. Mix lightly with a spoon, then by hand to form a smooth ball. Cover with cling film and let rise for about 1 hour or until doubled in size.
Prepare the dough: Break up the lievitino in a mixer. Add the flour and fresh brewer's yeast and mix at medium speed, gradually adding the milk little by little. Mix until the dough comes away from the edges. Add sugar, then increase speed and add eggs one at a time. Add softened butter gradually. Finally, add salt. Transfer dough to a floured counter.
First rising: With wet hands to prevent sticking, fold the dough a few times and place it in a bowl. Cover with cling film and let rise at room temperature for about 2 hours until doubled in volume.
Prepare the filling: Mix creamed butter and sugar well with a fork and set aside.
Shape the dough: Transfer the risen dough to a floured pastry board. Using hands and a rolling pin, roll it into a 30x50 cm rectangle. Spread the filling evenly with a spatula over the dough.
Form the rolls: Roll the dough tightly from the long side, compacting it to an even circumference. Cut six 6 cm rounds from the ends and one 8 cm round from the center.
Arrange and second rising: Butter a 22 cm springform pan. Place the large central round with the cut side up in the center, and arrange the smaller rounds around it. Leave space between them as they will expand during rising. Cover with cling film and let rise for 1 hour.
Prepare the syrup: In a saucepan, combine water and sugar. Bring to a boil while stirring, then turn off and set aside.
Bake the cake: Brush the risen dough with a mixture of egg yolk and fresh cream. Bake in a static oven at 180°C for 10 minutes, then reduce temperature to 160°C and bake for another 30 minutes.
Finish and serve: While still warm, brush the cake with the prepared syrup. Let cool slightly before serving.