Wash and peel the fresh yucca or thaw the frozen. Place in a small saucepan, and add water to cover and 1/2 teaspoon of the salt. Bring to a boil, reduce to a simmer and cook, covered, until tender, about 30 minutes. Drain in a colander and set aside to cool.
Preheat the oven to 350 degrees . When the yucca is cool enough to handle, pull each root apart and remove the large fibrous veins near the center, keeping the flesh in large chunks.
Melt the butter in a large skillet over medium-low heat. Cook the garlic until tender but not brown. Add the vinegar, the remaining 1/2 teaspoon salt and the pepper. Bring to a boil and add the yucca. Stir and mash with a wooden spoon until a lumpy mixture is formed. Transfer to a baking dish. Cover and bake 10 minutes. Garnish with the chopped parsley and serve immediately.
c.1997, M.S. Milliken & S. Feniger, all rights reserved