Preheat your oven to 200°C (400°F). Slice off the top 1cm (0.4 inch) of one whole head of garlic, exposing the cloves. Place it on a small piece of aluminum foil, drizzle with 1 tbsp (15ml) olive oil, and wrap it tightly.

Place the foil-wrapped garlic head on a baking sheet. Also, add the peeled and cubed potatoes to the same baking sheet, along with the second whole head of garlic (unpeeled).

Roast the garlic and potatoes in the preheated oven for 30-40 minutes. The potatoes should be tender when pierced with a fork, and the garlic cloves should be soft and fragrant. The unpeeled garlic head will turn golden brown and slightly caramelized.

Once the potatoes are tender, carefully remove the baking sheet from the oven. Let the garlic cool slightly until it's safe to handle. While still warm, squeeze the roasted garlic cloves from their skins into a small bowl. Mash them with a fork until they form a smooth paste.

Drain the boiled potatoes thoroughly. Return them to the warm pot over low heat for about 1 minute, shaking the pot gently to evaporate any residual moisture. This step is crucial for fluffy mashed potatoes.

Transfer the dried potatoes to a large mixing bowl. Add the softened 170g (12 tbsp or 3/4 cup) unsalted butter, the mashed roasted garlic paste, 2 tsp (10g) salt, and 1/2 tsp (2g) freshly ground black pepper.

Using a potato masher or a sturdy fork, begin to mash the potatoes and incorporate the butter, garlic, salt, and pepper. Mash until mostly smooth.

Gradually add the warmed 240ml (1 cup) heavy cream while continuing to mash and whip the potatoes. Continue mixing until the potatoes are incredibly smooth and creamy. Be careful not to overmix, which can make them gummy.

Taste and adjust seasoning with additional salt and pepper if needed. Serve hot.