Chocolate ginger cake with custard sauce - happy birthday hubby :-)

Ingredients

• 4 tbsp heaped - whole wheat flour
• 1 1/2 tbsp - oat flakes
• 6 tbsp - honey
• 6 tbsp - sunflower oil
• 1 1/2 tsp - baking powder
• 3/4 tbsp - cocoa powder
• a pinch of salt
• 100 grams - chocolate 55%
• 1/2 tbsp - crystallised ginger
• 2 1/2 tsp - dried ginger powder
• 1/2 cup - gingerale