Potato leeks and mushroom flan

Ingredients

• For The Potato ' Shell '
• 5-6 Large Potatoes ( boiled and peeled )
• 1 Teaspoon Dried Oregano ( use any or none if not handy )
• 2 Tablespoons Olive Oil .
• 1 Teaspoon Salt.
• The Filling
• 1 Packet Mushrooms ( chopped medium thick ).
• 2/3 Cup Chopped Leak ( 1/2 or a little less thick ).
• 2/3 Cup Milk.
• 2/3 Cup Cheddar Cheese ( grated ) I used a combination of Cheddar,Mozzarella and Gouda
• 3 Eggs.
• 1 Teaspoon Baking Powder.
• Salt and Freshly Crushed Pepper.