Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Heat butter and briefly sauté flour in it. Stir in milk, simmer for about 5 minutes. Season with salt, pepper and nutmeg.
Pour 1 teaspoon of sauce into each of four ovenproof moulds.
Cut toast and ham slices to fit the size of the ramekin. Toast bread. Layer bread, ham and approx. 1 tbsp. of sauce each in the ramekins until all ingredients are used up. Sprinkle with cheese.
Bake in a hot oven for about 10 minutes.