1 medium onion, thinly sliced (I used a mandolin)
2 tablespoons butter
1 teaspoon malt vinegar (lacking this, you can use cider vinegar)
1 teaspoon granulated sugar
1-1/2 to 2 pounds Melissa's Baby Dutch Yellow Potatoes, scrubbed, but unpeeled
1/3 cup cream
1 tablespoon butter
Salt and freshly ground black pepper, to taste
In a 9” saute pan, melt butter. Add thinly sliced onion and cook over medium high heat, stirring occasionally, until they become soft. Stir in the vinegar and sugar and continue to cook over medium heat until they have caramelized. While the onions are cooking, halve the potatoes and place them in a 2-quart saucepan and cover with water. Over medium-high heat, bring to a boil and cook until fork tender, 25-30 minutes. It helps to time things so that both onions and potatoes are ready at the same time, but if the onions get done beforehand, just turn off the heat and leave them on the warm burner.
When potatoes are fork tender, drain them, and return to the warm burner to allow for evaporation of excess water, a minute or so. You'll see a lot of steam come up during this process. Warm the milk and cream, and mash the potatoes in your preferred method, adding the melted butter and cream to yield a creamy texture. Fold in the caramelized onions and serve immediately.
http://pattietierney.blogspot.com/2016/01/rustic-mashed-potatoes-with-caramelized.html