Cookbook Sunday Dinner: Sweet Onion Gratin

If you’ve paid attention to the weather, you probably know that Seattle was bracing for the worst windstorm in history. The remnants of a typhoon were expected to bring hurricane-force winds and rain–we were hunkering down for a crazy storm, with expectations of power outages and downed trees. Then, well, the storm was a non-event; it moved a little more north and a little faster than expected. So, so much for the worst windstorm in history, at least this time. Growing up in Louisiana, I’ve been through enough storms that turned out to be exactly the opposite what was predicted, for better and worse, that I’ve learned to be cautious, take predictions for what they are, and don’t let one (or many) bad predictions give you a false sense of security.

Well, for now, all is quiet and normal (for the PNW)–drizzle, light wind, and grey skies setting the backdrop for lovely autumn leaves that didn’t get blown away in the non-storm. It’s a good day for watching football, wearing cozy clothes, and a warm comforting dinner that involves cheese, cream, sweet onions, and potatoes.

Cookbook Sunday dinner this weekend from Heritage was Sean Brock’s recipe for a sweet onion gratin. In the book, this is part of a recipe that includes an herb-marinated hanger steak but, since I don’t eat or cook beef, we had the gratin and a green salad with a lemon dressing to cut the richness of the gratin. If you can get Vidalia or Walla Walla sweet onions, use those–it’s not that time of year for me, so, I used whatever organic sweets were at the grocery store. This recipe, similar to the farrotto a couple of weeks ago, made me think the vegetables here are much smaller than in North Carolina! I used three large onions to get 2 pounds (~925 g) and the recipe called for 2. The recipe also specified 2 Idaho potatoes that were 1.5 pounds a piece; after we sliced up 3 good-size Idaho potatoes–the largest at the store–we had just over 2 pounds and this was a hefty amount of potatoes. So, we called it ‘good,’ and, also, we didn’t have anymore potatoes. I layered the gratin in a round baking dish and after an hour and half, rather than 1-hour cooking time specified in the recipe, the potatoes were still a bit al dente but close enough to done. By that time, it was 22:40 and we were hungry…so, a super late dinner for us tonight! Kind of reminiscent to when Skip and I first started dating and the first few years we lived together–we were lucky to eat dinner by 10:00 every night back then!

The gratin was tasty though a bit rich and won’t be something in the regular, weekly rotation but it’s a nice little treat and I’ll make it again for sure. It’ll be great for holidays, especially since you can make this a head of time.

Sweet Onion Gratin
Adapted from the Herb-Marinated Hanger Steak with Vidalia Onion Gratin and Steak Sauce From Heritage by Sean Brock
**Time: ~4.5 hours, start to finish

1 Stick (114 g) unsalted butter, plus more for greasing the dish
2-3 (926 g) Large sweet onions (like Vidalia or Walla Walla sweets)
1/2 C (~117 g) Heavy cream, whole milk, or a combination*
2 Tbsp (22 g) Kosher salt
1/2 C (~130 g) Greek yogurt or sour cream*
1 C (118 g) Gruyere cheese, shredded
1 C (70 g) Parmigiano-Reggiano, shredded
2-3 (974 g) Large Idaho potatoes*
1 1/2 C (188 g) Fresh bread crumbs, seasoned with salt & pepper


  • Heat the oven to 375 °F; butter an 8-inch round baking dish or gratin dish.
  • Using a mandoline, slice the onions paper-thin.
  • Heat a large Dutch oven over medium-high heat; add the butter and cook till just foamy, then add the onions and reduce hit to low.
  • Cook the onions for 1.5 to 2 hours uncovered, stirring occasionally, until soft and totally translucent. Add a little water as needed to prevent the onions from scorching.
  • Add the cream, bring to a simmer and then remove from heat.
  • Transfer the onion-cream mixture to a blender—do in batches if needed. Blend on high until very smooth, about 5 minutes.
  • Return the puree to the Dutch oven, add the salt and mix well.
  • Heat on low and bring the puree to a simmer. Remove from heat and stir in the yogurt or sour cream, 1/2 C Gruyere, and 1/2 C Parmigiano-Reggiano. The mixture will be very thick. Cover and keep warm.
  • Peel the potatoes and slice them paper-thin using a mandoline.
  • Add the potatoes to the onion cream. Being careful not to break the potatoes, gently combine the potatoes with the onion cream.
  • Spread the potatoes in the buttered dish.
  • Combine the seasoned bread crumbs with the remaining cheese and top the potato-onion cream mixture.
  • Bake for 1-1.5 hours or until the potatoes are fork tender.*



  • The original recipe calls for cream and sour cream as well as two 1.5-lb. potatoes, for a total of 3 lbs. potatoes. I used less but think the 3 lbs. of potatoes would have been better, though, that seems like a ridiculous amount!
  • The recipe said that the cooking time was 1 hour and the gratin took at least 1.5 hours—though, our potatoes might not have been thin enough. The next time I make this I’ll put it in a larger, more-shallow dish, and cover for the first 30 minutes or so.
  • The recipe didn’t specify letting the gratin cool before serving; I would let this set for 10-15 minutes, at least, next time.
  • Rather than combine all the potatoes with the onion cream, alternating layers of the potatoes and onion cream would ensure the potatoes remain intact.
  • This recipe would be great with other vegetable added in like thinly sliced cauliflower and/or broccoli stems.

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