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