Food / Nutella Mug Cake

75g Nutella
25g All purpose flour
3 tbsp milk
1 tsp cocoa powder
1/4 tsp baking soda
1 egg yellow (optional. Makes it soft) Pinch of salt

Whisk nicely. Fill mug till half only.
Microwave for 1 min and then 30 secs. Dust with icing sugar.