I have been cooking and refining this dish for years. The recipe is based upon one by Madame Germaine Carter whose 'Home Book of French Cookery' was a favourite in my teens, not only because of the recipes but also due to its narrative. Mme Carter and her co-authors were interned in a number of prisoner of war camps during World War II. During a winter of particular privation in 1941-42, a fellow prisoner suggested the book as a means to boost their flagging spirits. The book is long out of print, but copies are not hard to find.
I have included additional ingredients that you'll find in most 'authentic' recipes in the Suggestion section, but with the exception of the bread fried in bacon fat, I find them a distraction.
This dish is always better when made a day in advance.
For a great plate of roasted vegetables, you need a good balance of textures and flavours. Use too many root vegetables and it can be too sweet, though turnips will help offset that. Fresh herbs will give fragrance to the dish.
Use a combination of four or more of the following six categories: (1) potato and\or sweet potato, (2) squash and\or courgette\zucchini, (3) aubergine\eggplant, (4) root vegetables, (5) broccoli and\or cauliflower and (6) onions (red for colour) and a head of garlic.