Chopped fresh parsley or chives and extra butter, to garnish and finish
You'll want to start roasting the garlic 25 minutes before boiling your potatoes.Heat oven to 375ºF. Peel any extra skin off of the garlic bulb leaving only the last outer later of skin (you want to keep the bulb intact). Place the bulb onto a sheet of tin foil (about the size of a dinner plate), and drizzle a bit of olive oil over it. Bring bring the foil together over the garlic bulb to create a tent. Pinch a few edges to secure the tent, and bake for 40 minutes or until the garlic cloves are golden brown and nicely roasted. (Check on it at 25-30 minutes.) When done, remove the bulb from the oven and set aside to cool.
Place your peeled and quartered potatoes into a large pot and cover them with cold water. Add a pinch of salt. Place the pot over medium-high heat and bring the potatoes to a boil. Once boiling, bring the heat down to medium-low, cover, and simmer for 15-20 minutes or until the potatoes are fork tender.
When the potatoes are ready, drain them, and place them over medium-low heat. Let them sizzle for a few moments to remove any excess moisture. Then, remove from heat.
In a separate saucepan, melt 3 TBSP of butter. Add the chopped rosemary, bring the butter to a low simmer, and whisk for about 30-40 seconds to let the rosemary soften up and infuse the butter with some flavor. Remove from heat.
Squeeze all of the roasted garlic from their bulb into the pot with the potatoes. Then add the salt, pepper, rosemary butter, half and half, and Greek yogurt. Mash with a potato masher until you get the consistency that you desire. Add extra splashes of half and half or some extra Greek yogurt as needed.
Transfer the mashed potatoes to a serving dish, top with fresh chopped parsley or chives, and a few knobs of butter for extra buttery goodness.
If you have a food mill, you can run your potatoes through it to get the creamiest consistency. After running your potatoes through the food mill, you can then add the rest of the ingredients for mixing.