Heat the oven to 400°F. Slice the top 1/4 inch from the garlic head to expose the cloves, drizzle with oil, wrap in foil and roast for 35 to 40 minutes until soft. Cool enough to handle, squeeze out the cloves and mash smooth.
Near the end of roasting, cook penne in water with the tablespoon salt until 1 minute short of the package time. Reserve 1 cup pasta water before draining.
Melt butter in a large skillet over low heat and stir in mashed garlic. Add cream, milk, sauce salt and pepper and simmer gently for 2 minutes.
Add pasta and 1/4 cup reserved water and toss for 1 to 2 minutes until tender. Remove from heat and stir in Parmesan gradually.
Add more pasta water by the tablespoon if needed for a smooth coating and serve promptly.