My Goals

  • Rich, creamy texture

  • Delicate golden crust

  • Easy-to-accomplish attractive appearance

Pommes duchesse are thought to be named for a fictional French aristocrat with a penchant for potatoes: The recipe was dreamed up in the 19th century to encourage consumers to use more of the lowly spuds. The elegantly swirled individual mounds of eggy, buttery, yellow-tinged mashed potatoes with crisp crusts did the trick, and for years the dish remained popular, particularly on holiday menus.

So why aren’t pommes duchesse still on every special-occasion table? Well, their retro-luxe look requires a pastry bag, plus a bit of practice. What’s more, being rather petite, they cool rapidly. But I had an idea: Maybe baking the potatoes casserole-style would simplify things and help keep them hot.

We use a food mill to give the potatoes a creamy consistency before employing our foolproof method for mashed potatoes to prevent the spuds from getting overworked and gummy.

Traditional recipes call for stirring melted butter, eggs, half-and-half, nutmeg, salt, and pepper into peeled, boiled, and riced potatoes. I settled on 3 egg yolks, 8 tablespoons of melted butter, and ⅔ cup of half-and-half for 3½ pounds of buttery Yukon Golds. Following the test kitchen’s mashed-potato protocol, I poured the butter into the spuds first so its fat would coat the potatoes’ starch granules and protect them from being overworked and turning gluey.

The right ratio of protein and fat ensures that our coating turns golden brown and crisps in the oven, providing the perfect complement to the creaminess of the potatoes underneath.

After smoothing the potatoes into a buttered dish, I poured on a coating of beaten egg white, which is full of proteins that browned nicely after 30 minutes in a 450-degree oven. But the beautiful crust tore from the potatoes’ surface when I dug out a spoonful. Worse, the crust was plasticky instead of crisp and light. The culprit? The egg white proteins were linking to form a tough skin. I tried a coating of melted butter instead, which contains very little protein. This casserole’s surface crisped but had to be baked for 50 minutes to brown, which seemed excessive.

How about a mixture of butter and egg white? After 30 minutes, this batch emerged with a crisp, burnished crust. That’s because the fat in the butter acted as a hydrophobic barrier between the egg white’s protein molecules, reducing the formation of tough cross-links.

As a final touch, I scored the casserole with a knife, creating plenty of sharp edges to brown. These lush potatoes, with their crisp crust and majestic name, were fit for royalty.

Scoring it with a knife isn't the only way to help the casserole brown and crisp. Here are three other ideas.

Keys to Success

  • Rich, creamy texture

    Folding melted butter, followed by half-and-half and egg yolks, into Yukon Gold potatoes passed through a ricer delivers a velvety-smooth and decadent texture.
  • Delicate golden crust

    A combination of butter and egg white gives the gratin’s surface a beautifully browned, delicately crisp crust.
  • Easy-to-accomplish attractive appearance

    We use the side of a paring knife to score the casserole’s surface, giving it a beautifully polished look without the fuss of a pastry bag and star tip.