Peel butternut squash and remove seeds. With a sharp knife, carefully cut into sections to make 2-inch cube of uniform size.
Preheat oven to 350 degrees. Coarsely chop onions. Peel potatoes and cut into 1-inch cubes.
On a foil-lined baking tray(s), place the butternut squash, potatoes, onions and unpeeled garlic cloves. If using two trays, place onions and garlic cloves on one tray, separated from squash & potatoes. Drizzle extra virgin olive oil on all vegetables and mix with hands, coating well. Place trays in oven.
Roast onions and garlic for 20 minutes then let cool. Let butternut squash and potatoes roast for an extra 20 more minutes. Unpeel garlic cloves and chop into a few coarse pieces. Add onions and garlic to slow cooker insert.
Add roasted butternut squash and potatoes on top of onions and garlic. Add sage to mix, crushing between fingers if using dried. Pour in chicken broth and season with salt & pepper (or use Goya adobo).
Cook on low for 4 hours. Let cool slightly, then puree mix in blender. Serve hot with a little sour cream or a drizzle of olive oil.