Combine the potatoes and 1 teaspoon of the salt in a large saucepan over medium heat. Cover the potatoes with water and cook until fork-tender, about 20 minutes. Drain.
Return the potatoes to the pan and, over low heat, stir them with a fork or wire whisk for about 1 minute to dehydrate them. Add the cream, butter, garlic, and spinach. Stir to mix well. Add the remaining 1/2 teaspoon salt and the white pepper. Mix well. Serve immediately.
Preheat the oven to 400 degrees F.
Cut a small square of aluminum foil. Cut the garlic head in half and place on the foil. Drizzle both halves with the oil and season with the salt and pepper. Bring the ends of the foil together to make a small bag or pouch. Bake until the garlic is tender, about 45 minutes.
Remove the bag from the oven and carefully open it up a bit. Return to the oven for about 10 minutes more. Remove from the oven and let cool. Remove the flesh by squeezing each half head between your thumb and index finger. Use immediately or refrigerate in a little olive oil in an airtight container for 2 to 3 days.
Yield: about 2 tablespoons