Peel and wash the potatoes and cut them roughly into pieces. Cover and cook in little boiling salted water for about 20 minutes. Carve tomatoes crosswise, blanch with boiling water and peel the skin.
Heat the oil. Roast the pine nuts for about 4 minutes while turning them, take them out and chop them finely. Clean tomatoes and cut into fine cubes. Steam tomato cubes, except for a few for sprinkling, in the frying fat for 2-4 minutes.
Warm up the milk. Drain the potatoes and press them through a potato ricer. Add ricotta, pine nuts, except for a little bit for sprinkling, and milk and stir in. Fold in diced tomatoes. Season to taste with salt.
Arrange and sprinkle with pine nuts and diced tomatoes.