For the topping, melt the butter in a medium saucepan, then remove from the heat and whisk in the flour to form a paste (roux). Whisking all the while to prevent any lumps forming, gradually add the milk, return the pan to the heat and continue to whisk until the sauce has thickened to the consistency of custard and is gently bubbling. Stir in the nutmeg and saffron, season generously with salt and pepper and set aside for at least 30 minutes to cool.
While the topping is cooling, make the pasta. Pile the flour and salt onto a wooden board or into a bowl, make a well in the centre and crack in the eggs. Whisk the eggs lightly with a fork then, using your hands, mix everything together well to form a rough dough. Knead the dough together until all the pieces have combined and you have formed a velvety smooth lump of dough. (If the dough is looking a little dry, add a few drops of water. If it’s too wet, add a little extra flour.) Leave the dough in the refrigerator for at least 30 minutes to rest.
Once rested, divide the dough into 12 equal-sized pieces. Roll each out with a rolling pin on a lightly floured surface to a 7.5 x 15-cm (3 x 6-inch) rectangle. Cover with a damp clean tea towel to prevent the pasta from drying out and set aside.
Preheat the oven to 180°C / 350°F / Gas Mark 4.
For the sauce and filling, place two saucepans over a medium heat, adding 2 tablespoons of olive oil and half of the chopped red onion to each. Cook the onion, stirring, for 2–3 minutes until slightly softened, then add the passata and sage leaves to one pan and the chopped chicory to the other. Season both pans with salt and pepper and cook, stirring, for 15 minutes, until the tomato sauce has thickened and reduced slightly and the chicory has softened.
Bring a large saucepan of salted water to a boil. Working in batches, carefully lower the pasta rectangles into the water and cook for 60 seconds, then transfer to a bowl of iced water to prevent them from overcooking (be careful as you go, as the cannelloni are delicate and will tear easily).
Remove the pasta rectangles from the iced water, pat dry with kitchen paper and arrange on a clean work surface. Place a tablespoon of filling along the long edge of a pasta rectangle, then roll up gently to create a tubular shape. Carefully place the cannelloni in the prepared baking dish with the open edges down. Repeat with the remaining pasta rectangles.
Spoon the topping over the cannelloni and sprinkle over the breadcrumbs and Parmesan to finish. Bake in the oven for 25 minutes, or until the topping is golden and bubbling, then leave to cool for 10 minutes before serving.