Makes 4 servings.
For the soup:
For the roasted garlic oil:
To make the Roasted Garlic Oil: In a small saucepan over very low heat, combine the oil and garlic and cook until the garlic is a dark golden brown, about 45-50 minutes.
Let cool to room temperature, then strain. Store at room temperature.
To make the Cauliflower Soup: In a large saucepan or small stockpot over medium heat, heat the olive oil. Add the cauliflower and cook, stirring occasionally, until lightly browned, 5 to 7 minutes.
Stir in the onion, garlic, oregano, and sage and cook, stirring occasionally, until the onion is very tender and the entire mixture is beginning to brown, 8 to 10 minutes.
Add the stock, scraping up any browned bits on the bottom of the pot. Bring to a boil, lower the heat to a simmer, and cook until the cauliflower is very tender, about 5 minutes.
Working in batches, if necessary, transfer the soup to a blender or food processor, or use an immersion blender, and puree (be careful—the mixture will be hot), scraping down the bowl or jar as necessary.
Reheat the soup if necessary and add salt and pepper to taste. Serve hot, drizzled with the Roasted Garlic Oil to taste and a handful of crunchy croutons.