I saw this on the Barefoot Contessa TV show and thought this would be so tasty. It was! I made it with chicken and steak, but honestly this would be great alongside any dish. Very easy and pretty perfect. This was how I prepared it. It served 6 very well, and it could probably serve 8 – 10 as a side dish. A perfect dish for Thanksgiving or Christmas or any dinner party.
Ingredients:
2 – 2 1/2 lbs. Yukon gold potatoes
2 medium size yellow onions
3 tablespoons olive oil
2 tablespoons whole-grain mustard
Kosher Salt – about 2 teaspoons
Freshly Ground Black Pepper – a few good grinds of the pepper mill
Directions:
Preheat the oven to 400 degrees.
Cut the potatoes in quarters, and then I cut them again, I found they crisped up better smaller. Place on a very large sheet pan, do not crowd. I actually used two baking sheets for this amount of potatoes. Remove the ends of the onions, peel them, and cut them in half, slice them crosswise in app. 1/4 ” slices to make half rounds. Toss the onions and potatoes on the sheet pan. ( I also sprayed pans generously with Pam cooking spray)
In a separate bowl, with a wire whisk mix the mustard and the olive oil, and pour over potatoes. With clean hands I mixed up everything on sheet pan, then sprinkled 2 teaspoons kosher salt, and freshly ground black pepper on the potatoes and mixed again. I baked for about an hour at 400, or until the potatoes were lightly browned on the outside and tender on the inside. I prefer a little crispy, do them however you like. I tossed a few times with a metal spatula during cooking process.
Taste for salt, and you can always add more salt at the end. 
Cooking with Candi 