4 pounds russet potatoes , peeled, quartered, and cut into 1/2-inch pieces
12 tablespoons (1 1/2 sticks) unsalted butter , cut into pieces
12 garlic cloves , minced
1 teaspoon sugar
1/2 cups heavy cream
1/2 cup water
Salt and pepper
Place cut potatoes in colander. Rinse under cold running water until water runs clear. Drain thoroughly.
Melt 4 tablespoons butter in Dutch oven over medium heat. Cook garlic and sugar, stirring often, until sticky and straw colored, 3 to 4 minutes. Add rinsed potatoes, 1 1/4 cups heavy cream, water, and 1 teaspoon salt to pot and stir to combine. Bring to boil, then reduce heat to low and simmer, covered and stirring occasionally, until potatoes are tender and most of the liquid is absorbed, 25 to 30 minutes.
Off heat, add remaining butter to pot and mash with potato masher until smooth. Using rubber spatula, fold in remaining half-and-half until liquid is absorbed and potatoes are creamy. Season with salt and pepper. Serve.