Preheat oven to 400°F (or 375°F in a true convection oven)
Wash potatoes and dry them.
Peel carrots, beets and onion.
Cut carrots in 1" chunks, slice beets and onions into thick wedges. Place in a large bowl.
Cut potatoes into quarters (leave the skin on). Add to the bowl. Your vegetables should all have roughly the same size so that they cook evenly.
Drizzle 2 tbsp olive oil into the bowl, add salt, pepper and herbes de Provence. Toss well, preferably with your hands so that all vegetables are nicely coated.
Line a baking sheet with parchment paper. Spread vegetables well to make sure the sheet is not overcrowded.
Place in the oven. Check after 35 minutes and continue baking another 5 minutes if needed until all vegetables are nicely browned.
Note that there is usually no need to toss them during cooking. The sheet side will be a bit more browned than the top but they will all come out beautifully as long as the sheet is not overcrowded.
Optional: heat 1 tbsp olive oil in a skillet. Add 1 tbsp sliced sage leaves. Drizzle over vegetables before serving.
Notes
Nutrition facts do not include optional olive oil for topping.