Beetroot au Gratin

Peel the beetroot and cut into thick slices. Arrange these in a greased pie-pan. Melt the butter ( or marg) in a saucepan, sprinkle in the sieved flour, stir until smooth, then add the milk, slowly, and simmer until the mixture thickens. Take off the heat and stir in the vinegar, drop by drop, and add the grated cheese and seasonings to taste and stir until the cheese has melted. Pour this mixture over the beetroot, scatter breadcrumbs over the top, and bake in a hot oven for about 15 minutes.