Preheat oven to 425°F (220°C)
Slice the top off the garlic bulb to just expose the cloves. Place on a piece of tin foil, drizzle with a bit of avocado oil, salt and pepper then wrap garlic in the foil. Place on a small baking sheet and pop it into the oven. Roast garlic for 50-60 minutes until it looks caramelized and golden. Set aside.
Meanwhile, slice potatoes in half, then cut the halves into quarters. You should end up with roughly 1 ½ inch (4cm) pieces.
Place potatoes in a medium pot. Fill pot with water and bring it to the boil. Cook until potatoes are super tender and skins are loose, about 15-20 minutes. Drain and then place back in the pot, off the heat.
Add beans, salt, pepper, milk and butter to large mouthed blending cup or bullet. Carefully squeeze garlic cloves out of their bulb and into the cup. Blend with an immersion blender until totally smooth.
Add creamy bean mixture to potatoes and mash until well-combined. Taste and adjust salt and pepper as desired. Scoop into a serving dish and garnish with chives.