Preheat the oven to 180 ° C. Grease a 22 springform pan.
Mix the butter and sugar together until creamy. Add the eggs one after the other, stir in for half a minute each time. Fold in the flour and sour cream.
Pour half of the batter into the cake pan. Mix the brown sugar, hazelnuts and cinnamon well, sprinkle on the dough and pour the second half of the dough on top. Bake for 45 minutes. Let cool in the mold for a few minutes.