Melt the butter in a saucepan over a medium high heat. Once melted, stir in the flour. Gradually add the milk, stirring all the time, and cook for 5 mins, until thickened. Add 80g of the cheese and stir until completely melted into the sauce.
Drizzle Marmite into the bottom of 4 ramekins, and top with the cheese sauce. Crack an egg on top of each, and sprinkle with the remaining cheese.