Preheat oven to 425F. Line a large baking sheet with parchment paper.
When cutting the florets off the head of cauliflower, make sure they're all about the same size. Keep in mind that the larger the florets, the longer it will take to roast, the smaller the florets, the shorter amount of time they'll need in the oven.
Spread the cauliflower florets evenly on the baking sheet and drizzle with 1/4 cup of olive oil. Use your hands to rub the oil onto each floret.
Trim about 1/4 inch off the top of the garlic bulb to expose the garlic cloves. Remove any loose, white papery covering but leave enough that the bulb will still stay together. Place the bulb in the center of a piece of aluminum foil. Drizzle a tablespoon of olive oil over the bulb and use your hands to rub it over the entire garlic. Wrap the garlic in the aluminum foil and place on the baking sheet with the cauliflower.
Place the baking sheet on the center rack of the oven and roast for 30 to 40 minutes or until the cauliflower is slightly browned and tender.
Use tongs to transfer the cauliflower to a high speed blender or food processor. Unwrap the garlic from the aluminum foil and either use a small fork to remove the garlic from the paper or gently squeeze the bottom of the bulb to push out the cloves. Add to the blender along with the salt.
Blend the mixture and with the motor running, slowly add the vegetable broth until the mashed cauliflower is to your desired consistency (I like to start off adding 1/4 cup of vegetable broth and then slowly add more as needed). Stop to scrape down the sides of the blender jar as needed.
Either pipe the roasted mashed cauliflower onto the top of the meatloaves or put a big dollop on top and use a fork to fluff it up and make it look pretty.
The mashed cauliflower can be stored in an airtight container for 3 to 5 days in the refrigerator.