Preheat oven to 200˚C and prepare 4 ramekins on a baking tray.
Blanch the spinach quickly by placing it in a colander in the sink. Pour over a freshly boiled kettle of water and then immediately rinse with cold water. Squeeze all the water out and set aside.
In a large frying pan over high heat sauté the mushrooms in a drizzle of olive oil until golden brown. Set mushrooms aside.
In the same pan add in the 2 tbsp butter, the leeks and garlic and cook until the leeks are tender and the garlic is fragrant.
Sprinkle in the flour and stirring constantly cook the flour for a few minutes. Pour in the milk and stir until smooth. Bring to a simmer. Season with salt, pepper, mustard and nutmeg.
Once the mixture is thick, remove from the heat. Stir in the mushrooms, spinach and Parmesan.
Divide mixture between ramekins and create a well in the centre of each one.
Crack an egg into each well and bake for 10-15 minutes until the eggs are cooked to your liking.
Sprinkle with some crushed pink peppercorns and serve.