Baked Cabbage and Potato Gratin

Steps

1. Trim off the base of the cabbage to make it sit up, then peel away thin layers using a knife along the natural seams.
2. Release the core with a small V cut and proceed with brief strokes until all shreds are separated. Place them in a large bowl.
3. Boil water and pour just enough to cover the shredded cabbage; weigh down with tongs and leave for ten minutes to blanch.
4. While the cabbage blanched, slice an onion pole to pole and shave thin half rings.
5. Warm a skillet over medium heat with olive oil. Add the cut onions and stir occasionally until they turn pale.
6. Add red bell pepper ribbons to the pan; allow them to receive the center of the pan first before folding them with the onions.
7. Spread the vegetables in a flat layer, adding a teaspoon of water if the surface is dry, then season lightly with salt and black pepper.
8. Stir the vegetable mixture on low heat until tender. Remove from heat.
9. Scrub and trim potatoes; grate them using the coarse side into a bowl of cold water to rinse off starch.
10. Let the potato shreds soak in cold water for ten minutes while the pan continues to cook gently.
11. Drain the blanched cabbage well, shaking the bowl to allow steam to escape. Spread the sweet and sticky onion/pepper mixture onto the cabbage and fold until colors are bright.
12. Squeeze the soaked potatoes dry using a towel until the water is clear but some starch remains at the bottom of the bowl.
13. Add dried herbs (dill, parsley, or mix) to the large bowl with the cabbage and vegetables. Season with salt, black pepper, dried garlic powder, sweet paprika, and rosemary.
14. Stir slowly until spices are well balanced. Drizzle with a thin thread of olive oil and taste, adding lemon juice if desired.
15. Spoon the mixture into a baking dish, smoothing gently to level the top.
16. Whisk three eggs in a fresh bowl until ribbons drop back and disappear; add milk or plant milk and whisk again.
17. Add a trickle of olive oil to the custard. Taste and season with salt if needed.
18. Fluff the egg mixture two or three times, whisking from sides towards the center until it is pourable but not too thin.
19. Shave fresh dill finely and sprinkle into the bowl; fold gently with a spatula.
20. Pour the custard gradually over the hot vegetable base in the baking dish. Place on the middle rack for 30 to 35 minutes, or until edges pull back and center is set.
21. Dice three ripe tomatoes and place them on a towel if very juicy.
22. Grate 100 grams of cheese (Mozzarella, Gouda, Cheddar) into shreds. Layer the shredded cheese over the baked dish.
23. Return the dish to the oven for a short finish until the top is molten and golden brown.
24. Prepare the cold sauce: mix mayonnaise, sour cream/yogurt, finely grated cucumber (wrung out), chopped dill, microplan garlic, salt, pepper, and lemon zest if desired.
25. Pull the casserole from the oven to rest. Top with fresh tomato chunks and a rub of Italian spices.
26. Serve the dish with a spoonful of cold sauce on the side.