Peel the sweet potato and chop it into medium size dices and cut the garlic in small pieces. Put a big pot on the stove over medium high heat with some oil, and put the sweet potato and garlic there and cook for 3 minutes until the turn slightly golden brown.
Add in enough water to cover the pieces of sweet potato plus 1/2 tsp salt, let it boil and then lower the heat to let it cook (with no lid on) for 9-12 minutes until it turns soft.
Once the sweet potato is fully cooked (you´ll know it when a fork easily slides into it), drain the water and put the pieces back in the potl. Now, mash it with a potato masher until you have a smooth paste.
While the sweet potato is still hot add in the rest of the salt, butter, heavy cream and pepper. Mix using a fork for all the ingredients to come together.
Serve while hot with some spring onion or parsley if you wish. If you have some leftovers you can store them in the fridge for up to 4 days.