Preheat the oven at 180°C
Peel the potatoes
Wash eggplants and zucchinis
Cut all the vetables into strips.
Butter the ovenproof dish and sprinkle it with garlic.
Have one layer of potatoes, then one of eggplants and one of zucchinis. Sprinkle with salt, pepper and garlic.
Repeat this step twice in orde to obtain 3 layers of each vegetable.
Then pour the whole ketchup in the dish and sprinkle of grated Gruyère cheese.
Oven at 180°C for 45 minutes.
Check the cooking process using the tip of a knife.