Mushroom and cheese tart: A breakfast you can have for dinner

Ingredients

• 125 g butter
• 2 tbsp sugar
• 2 tsp oil
• 2 cups flour
• 2 tsp baking powder
• 1 egg
• 1 tin creamed mushrooms (or freshly made by you)
• 50-100 g grated cheese
• 25 g butter
• 2 tbsp flour
• 1 small onion, chopped
• 1 egg, separated
• 125 ml milk
• ½ chicken stock cube or brown onion soup powder
• salt and pepper to taste