To prepare potatoes, place potato and garlic in a Dutch oven; cover with water. Bring to a boil, and cook for 20 minutes or until very tender. Drain well; return to pan, and place over medium heat. Stir in 3/4 cup milk, 1 tablespoon butter, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Mash the potato mixture with a potato masher. Cook for 5 minutes or until thoroughly heated. Keep warm.
To prepare gravy, melt 1 tablespoon butter in a saucepan over medium heat. Add flour, and cook for 1 minute, stirring constantly. Gradually add 1 cup milk, 1/2 teaspoon pepper, and 1/4 teaspoon salt; stir with a whisk. Bring to a boil; stir constantly. Reduce heat, and cook 5 minutes, stirring occasionally. Serve gravy with potatoes; sprinkle with chives.