Bring 3-4 l salted water (1 teaspoon salt per litre) to the boil. Cook the pasta until al dente according to the package instructions. Drain and let drain well.
In the meantime clean and wash the broccoli and divide it into small florets. Cook in boiling salted water for about 3 minutes. Add peas for the last 1-2 minutes. Lift out the vegetables and let them drain. Put vegetable cooking water aside.
Grate rolls into crumbs and mix in a bowl with oil and some sea salt.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Grease a large casserole dish. Peel and finely dice the shallots. Melt 3 tablespoons of butter in a pot and sauté the shallots for about 1 minute. Stir in flour and sauté briefly. Add 200 ml vegetable cooking water and milk, stirring constantly. Bring to the boil and simmer for about 5 minutes. Season sauce with salt and pepper. Grate cheese and melt in the sauce while stirring.
Put the pasta, vegetables and cheese sauce into the casserole dish and mix well. Spread the crumb mixture evenly over the top. Bake the casserole in a preheated oven for about 25 minutes until golden brown.