Heat an extra large skillet over medium-high heat and add vegetable oil to the pan.
When the oil is hot, add all of the vegetables to the skillet and sauté for about 15-20 minutes, leaving veggies alone long enough to develop browning, but not long enough to burn. When veggies are soft and have developed some nice browning color, add about a 1/2 cup broth to the pan and scrape any browned bits from the bottom of the pan.
Transfer veggies and liquid from deglazing into a high speed blender with one cup of vegetable broth and blend until smooth. You may have to do this in batches.
Once all the veggies are in puree form, combine veggie puree and the rest of the broth in a pot. Bring soup to a simmer and salt and pepper to taste. Allow the soup to simmer and flavors to combine for about 15-20 minutes, stirring often.
Serve the soup in bowls and drizzle each with the rosemary oil. Enjoy!