Preheat oven to 180 C / Gas 4. Butter and flour a 23cm springform tin. Sieve together the flour, baking powder, bicarbonate of soda and salt; set aside.
In a large bowl, cream together the butter and 330g dark brown soft sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla and 1 teaspoon cinnamon. Beat in the flour mixture alternately with the milk. Fold in cranberries and hazelnuts.
Pour batter into prepared tin. Mix together 75g dark brown soft sugar, 4 tablespoons caster sugar and 1 teaspoon cinnamon; sprinkle over cake and swirl through the batter.
Bake in preheated oven for 75 to 80 minutes or until a skewer inserted into the centre of the cake comes out clean. Allow to cool.