You can try it at a higher temp. I usually roast veggies at 400F.
Thanks, I’ll do that next time. 350 took forevever.
one more thing to reduce cook times and increase flavors
one single layer. dont pile stuff into the pan just spread it out.
The first question when cooking anything but dessert, though the residents of Gilroy, California may disagree with even that limitation.
I enjoyed that dish so much that I decided to make it again today (with the addition of a red bell pepper):
I think I cut up about 7 red potatoes, 2 large yellow onions, a bag of carrots and 1 red bell pepper. Then poured on some olive oil, followed by garlic salt and black pepper. Lastly, I added 5 slices of real butter.
It’s now in the oven at 395 for 50 minutes. I’m guessing it’ll take longer than that, but it’s a good start.
My apartment smells yummy right now!
I think you’re looking for “Umami” and there are several ways to get it. My “go to” is always a tiny drop or two of dark sesame oil. Really, use very little until you are used to it, but /I use it in many vegetarian dishes to add that carnivore oomph without meat.
Portabellos are an excellent suggestion, as you can cut them in large chunks and they’ll stand up to the cooking process you describe. You mention adding beef broth, so perhaps you are not against shaving some parmesan on top just before it’s done. Just a touch, and let it brown.
Other options: drizzle with a vinaigrette made of olive oil mixed with some balsamic vinegar, not straight olive oil; helps to caramelize the vegetables and add more of a meaty flavor. Also you could add some chopped raw bacon to the vegetables (didn’t notice if someone already mentioned either of these).
You can add a small turnip or half of a big turnip to the veggie mix, too. My grandfather didn’t like turnips, so my mother never cooked them. I decided to give them a try as an adult, and discovered that I like them, especially in soups.
Roasted roots aren’t roasted roots without a turnip or three. Around here we also boil them up with potatoes ala Paula Deen.
I’m not a turnip fan. Except as part of Roasted Roots. Ditto for beets, and for parsnips. And I can’t tell you how many people who don’t like turnips, beets and parsnips like my Roasted Roots! 
Yea, something along this line here. I think I once saw a chef who had his own special “meat powder” that was not for use on meat, but rather as an enhancer for ingredients like roast vegetables that he wanted to make meatier. It kind of reminded me of freeze dried meat essence, sort of like coarsley ground bullion, and I wouldn’t be surprised if there wan’t some monosodium glutamate in there.
While you’re at it, why not just put a few marrow bones between the vegetables, and let the fat melt into the baking dish? Then you can keep the marrow for yourself! Spread on baguettes for a little snack 
Because lone bones are not fatty enough. The marrow is self contained. You need lard and meat powder.
Cumin and coriander seeds - roughly crushed - sprinkled over.
Parsnip and garlic (unpeeled) are good additions.
If adding mushrooms (I don’t after experimenting) you need to add them at the end, ditto with whole cherry tomatoes. 30 mins max.