Wash the potatoes and cook for 20-25 minutes in boiling water. In the meantime, dice the bacon and drain it in a pan without fat. Peel and wash the carrots and cut them diagonally into pieces. Clean broccoli, cut off florets and cook both in boiling water for about 5 minutes.
Collect 150 ml vegetable water and stir in the stock. Melt the fat in a saucepan, dust with flour and sauté. Pour in the milk and vegetable stock. Simmer for about 5 minutes and season with salt and pepper.
Drain the potatoes, rinse and peel them. Put the vegetables and potatoes in an ovenproof dish and add the sauce. Sprinkle cheese over the casserole. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 20-25 minutes.