Sausage, Leek, and Potato Pie

Ingredients

• 3 leeks (chopped into 2 cm slices)
• 1 onion (diced)
• 1 tsp minced garlic
• 2 tsp olive oil
• 4 yellow potatoes
• 1 lb sausage (cooked and sliced into 1/2 inch slices)
• 1 tbsp chopped parsley
• 3 tbsp butter
• 3 tbsp flour
• 1/2 tsp salt
• 1/2 tsp black pepper
• 2 cups milk
• 1 1/2 cups shredded cheddar cheese
• 1 sheet puff pastry (thawed)
• 1 egg