Preheat oven to 400º F.
Place the chopped parsnips into a large bowl. Sprinkle with salt, pepper, and freshly chopped rosemary. Drizzle 1 TBSP of olive oil on top and toss to coat. Transfer the parsnips to a baking sheet and evenly distribute them over the surface.
Remove any extra papery outer layers of the garlic bulb, leaving the skins of the individual cloves of garlic intact. Cut about 1/4 inch from the top of the cloves to expose the tips of the individual cloves. Place the garlic head, cut side up, onto a square of tin foil. Drizzle the rest of the olive oil (1/2 tablespoon) over the bulb to oil up the exposed cloves of garlic. Then, close up the foil creating a tent for the garlic bulb. Placed the wrapped bulb onto the middle of the baking sheet along with the parsnips.
Bake the parsnips and garlic for 30 minutes, or until the parsnips are tender and the garlic is a pasty consistency—enough so you can squeeze it out of the bulbs.
While the parsnips and garlic roast, start your onions. Heat 1 tablespoon of olive oil into a sauce pot or Dutch oven over medium heat and add 2 tablespoons of butter. Once the butter has melted and is foamy, add the diced onions and bring the heat to medium-low. Simmer, stirring often, for about 20 minutes or until the onions are soft and golden in color, slightly caramelized. Add the broth, and bring the heat to medium-high until the broth simmers. Once the broth is simmering, remove from the heat and set aside.
Place the roasted parsnips into a high-powered blender, then add the roasted garlic by gently pressing the garlic out from the cloves. Transfer the broth and onions to the blender, and blend until the mixture is silky and smooth. (Depending on the size of your blender, you may have to do this in batches.) If you want a more liquidy soup, just add a bit more broth until you get the consistency you want.
Serve the soup hot and garnish with toasted pine nuts, microgreens, crushed root chips, and/or a drizzle of cream.