Wash the potatoes and cook for 15-20 minutes in boiling water. Then rinse with cold water and peel. In the meantime peel the onion. Wash, clean, quarter and seed the tomatoes. Cut tomato pulp, onion and bacon into small cubes.
Debark and crumble the toast. Drain mozzarella and cut into slices. Wash basil, chop leaves roughly. Melt butter. Sauté onion cubes and bacon in it. Add flour and sauté.
Add cream and stock while stirring constantly and bring to the boil. Season with salt and pepper. Stir in diced tomatoes and basil. Divide the potatoes, sauce and mozzarella into casseroles. Sprinkle with toast crumbs.
Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 15-20 minutes.