Heat sweet potatoes, parsnips and enough water to cover in 5-quart saucepan over high heat; boil. Reduce heat to low; simmer, covered 15 minutes until vegetable are tender. Drain; keep warm.
Meanwhile, in 1-quart saucepan over high heat, heat milk and garlic cloves just until boiling. Reduce heat to low; cover and simmer 15 minutes to blend flavors.
Melt butter; add leek in small skillet over medium heat. Cook, stirring occasionally, until leek is tender.
Mash cooked potatoes and parsnips with milk mixture in large bowl, until smooth. Stir in leeks, TABASCO® Green Sauce and salt.
Makes 6 servings.