Spiced Brown Sugar Meringue Cake

• 4 eggs
• 2 egg whites see note
• 450 gr packed brown sugar
• 400 ml buttermilk see note
• 375 gr all purpose flour
• 250 gr sugar
• 170 gr margarine
• 60 gr black walnuts (chopped)
• 5 gr baking soda
• 4 gr cinnamon (ground)