Mashed Boniato with Onions (Pure de Boniatos con Cebollas) Recipe

• 1 1/2 pounds boniato (tropical sweet potato)
• 1 1/2 pounds red-skinned potatoes
• Salt and freshly ground black pepper
• 2 tablespoons vegetable oil
• 1 1/2 cups thinly sliced red onions
• 1/4 cup sherry vinegar
• 2 cups heavy cream
• 1/4 cup roasted garlic (see note)

1. Peel the boniato and the red potatoes and chop them into large pieces; place each in a separate container of water.
2. Fill two medium saucepans with water and bring to a boil over high heat. Add some salt and cook the boniato and the potatoes separately until fork tender.
3. In a medium sauté pan over medium-high heat, add the oil and cook the onion until caramelized. Deglaze pan with sherry vinegar and season with salt and freshly ground pepper.
4. In a medium saucepan over medium heat, reduce the heavy cream by half. Whisk in the roasted garlic and season with salt and pepper.
5. In a large stainless-steel mixing bowl, combine the potatoes and onions and add the cream a little at a time while mashing the potatoes. Season the mixture with salt and pepper. The mashed mixture can be kept in the stainless-steel bowl covered with aluminum foil over a pot of simmering water for 1 hour.

Note: To roast the garlic, put the heads of garlic in aluminum foil and roast at 400°F until soft, about 45 minutes.

SOURCE: http://www.chow.com/recipes/10616-mashed-boniato-with-onions-pure-de-boniatos-con-cebollas