Zebra Butter Cake 斑马纹牛油蛋糕

1磅蛋糕模 1 lb loaf tin 22 x 11 x 6cm  

(A)
• 35g butter 牛油
• 35g milk 牛奶
• 10g granulated sugar 糖
• 2 egg yolks, cold 蛋黄 (冷)
• a pinch of sea salt 一小撮海盐
• 1/2 tsp honey or vanilla extract 蜂蜜或香草精
• 35g cake flour 低筋面粉

(B)
• 2 egg whites, cold 蛋白 (冷)
• 1/2 tsp distilled vinegar 醋
• 35g granulated sugar 糖

(C)
• 1 tbsp dark cocoa powder 可可粉
• 2 tbsp hot water 热水
or just adding 1 tbsp dark cocoa