Pre-heat the oven to 425°F.
Drizzle the garlic with EVOO and season with a little salt. Wrap tightly in foil and roast the garlic until soft, 45 minutes. Let cool to handle.
Combine the garlic, half-and-half, salt, white pepper and a little nutmeg in a blender and puree. Adjust the seasoning, to taste.
In medium size skillet over medium heat, melt the butter and whisk in the flour. Cook for 1 minute, add the half-and-half mixture and bring to a bubble. Separate the spinach with your fingertips as you add it to the sauce. Simmer at a low bubble to thicken, 20-25 minutes.