Lightly toss garlic in olive oil. Place on baking sheet in one layer and roast for 30 minutes until golden brown. While still hot, puree roasted garlic in blender or food processor.
Meanwhile, wash potatoes in cold water. Peel if desired and cut large potatoes into quarters. Place into a large stockpot and cover with water. Bring to a boil, cook until soft. Drain and return to pot. Add pureed garlic, salt, and yogurt. Mash until combined. Gradually add skim milk until desired consistency is reached. Serve with herb gravy.
For Gravy
Combine all ingredients with exception of cornstarch and cold water in a saucepot. Bring to a boil. Combine cornstarch and cold water in a small bowl and mix until smooth. The cornstarch will settle to the bottom of the bowl if the mix sits, so be sure to mix again before using.
Once boiling, gradually add cornstarch and water mix until gravy is thickened. Repeat the cornstarch process if needed until the desired consistency is reached. Serve over garlic mashed potatoes.