Gratin of Potatoes & Porcini Mushrooms in Cream

This potato gratin gets its remarkable depth from dried porcini mushrooms soaked for 90 minutes until they release that intensely earthy, woodsy liquid that becomes the backbone of the entire dish. Both the rehydrated mushrooms and their soaking liquid go into the cream base, so the porcini flavor permeates every layer of potato.

The stovetop pre-cook before baking is what sets this apart from a typical gratin dauphinois. Thinly sliced potatoes simmer in the porcini-cream mixture for about 15 minutes until they start to soften, absorbing mushroom flavor the whole time. By the time the dish hits the oven, the potatoes are already partially tender and deeply seasoned, not just floating in cream waiting to cook through.

Sauteed shallots add a sweet, mild allium note that rounds out the mushroom’s earthiness. A final broil at the end creates that golden, bubbling crust on top that makes a gratin irresistible. This can be assembled a full day ahead and refrigerated before baking.

Chef Tips

• Strain the porcini liquid through paper towels. Dried porcini always have grit. That soaking liquid is liquid gold, but only if you filter out the sand.
• Slice the potatoes uniformly thin. A mandoline is ideal. Uneven slices mean some are mushy while others are still crunchy after baking.
• Taste the cream mixture before transferring to the baking dish. Adjust salt and pepper now, because it’s harder to fix once baked.
• Watch the broiler closely. Three minutes is all it takes. Cream and cheese (if added) go from golden to blackened fast.

Variations

• Add Gruyere on top before broiling for a cheesy crust that complements the porcini beautifully.
• Mixed mushroom version: Add sliced fresh cremini or shiitake mushrooms alongside the porcini for more variety in texture.
• Thyme or rosemary: A sprig of either simmered in the cream adds an herbal layer that pairs naturally with mushrooms and potatoes.