Place cut potatoes in colander.Rinse under cold water until water runs clear.Drain thoroughly.
Melt 4 tbsp butter in Dutch pot over medium heat. Cook garlic and sugar,stirring ofter until sticky and straw color 3-4 minutes.Add potatoes
1 1/4 cup half and half,water,and 1 tsp salt to the pot and stir to combine.Bring to a boil,then reduce heat to low and simmer,covered and stirring occasionally,until potatoes are tender and most of liquid is absorbed 25-30 minutes.
Off heat ,add remaining butter to pot and mash pototoes until smooth.Using rubber spatula,fold in remaining half and half until liquid is absorbed and pototoes are creamy.Season with salt and pepper.