Place the water in a large stock-pot over high heat.
Quarter the potatoes and add them to the stock-pot.
Cover with water by about an inch. Bring to boil and then reduce heat until the water is simmering.
Cook the potatoes about 15 – 20 minutes, until slightly soft in the middle. They should give when squeezed.
While the potatoes are cooking add the olive oil to a small skillet over medium high heat.
When the oil is hot add the spinach and reduce the heat to medium. Cook for about one minute until the spinach is wilted.
Remove from heat and drain water.
Add butter, buttermilk, milk and salt to the potatoes.
Mash the roasted garlic in a small dish until smooth.
Add the garlic to the potatoes and mash until creamy and the roasted garlic is well blended.
Fold in the cooked spinach.
Add ground black pepper to taste, then serve.
