This is as easy as chopping an onion, some broccoli, and cauliflower.
Vegetables: my favorites right now are broccoli and cauliflower, or asparagus (when in season).
Directions: preheat the oven to 400 F, while chopping the vegetables. Put them in a large glass baking dish. Put them in the oven for 20 minutes. stir. Cook another 20 minutes. Now you decide if you want to cook them longer. This depends on your oven and your preferences. Note that they will continue to cook as they cool. But if you like them softer and sweeter, you can leave them in another 10-20 minutes, or turn off the oven without removing them and let them continue to cook as the oven slowly cools. After a few experiments you'll know what you prefer.
Note on onions: The vidalias are the most sweet, and the reds are least. They will all sweeten up with roasting.
Note on not adding liquids. Notice I didn't include oil or water. The onions release water as it cooks. It's possible if you didn't use onions, maybe you'd want 1 T of water. But the veggies release liquid too. Anyway, for this recipe, no added liquids are needed!
Feel free to add any seasonings or salt if you you'd like. If I'm taking my veggies to a potluck, I'll usually add salt since most people are used to eating a lot of salt. Otherwise, even though I do eat some salt in my diet, I don't find any desire to add salt to these when making for myself, as they are flavorful and sweet all on their own.
Here are my starting ingredients: