Black Forest Chocolate Fudge Cake

• 2 eggs
• 1 egg (white)
• 1 prune puree see note
• 1 sprig mint for (garnish)
• 325 gr packed brown sugar
• 270 gr pitted unsweetened dark sweet (frozen)
• 250 gr cake flour
• 240 ml boiling water
• 180 ml nonfat milk
• 100 gr walnuts (chopped toasted)