Heat 2 tsp of oil in saucepan over medium-high heat. Cook mushrooms for 5 minutes, until golden brown. Season and remove from pan

Heat 1 tbsp of oil in the pan over medium heat. Cook leek for 4 minutes, until soft. Stir in flour and cook for 1 minute. Gradually add milk, stirring to prevent any lumps. Cook for 3 minutes, stirring, or until mixture boils and thickens. Stir in the mustard and 1/3 cup of the cheese. Season to taste

Spread leek mixture evenly onto 2 slices of bread. Top with a layer of mushrooms, spinach and the remaining cheese. Sandwich together with remaining bread. Toast in a sandwich press for 4 minutes, until golden brown and cheese has melted

Meanwhile, heat remaining 2 tsp of oil in a non-stick frying pan over high heat. Crack the eggs into the pan and cook for 2-3 minutes, until whites are set and yolks are still runny

Top each sandwich with a fried egg to serve. Scatter with chives and baby herbs