Name: Fennel and Potato Au Gratin
Prep time: 15 min
Cook time: 2 h 15 min
Total time: 2 h 30 min
Yield: 10 servings
Ingredients: 2.5 lbs Russet Potatoes; 2 bulbs fennel; 4 oz pancetta, chopped; 3 tablespoon unsalted butter; 4 cloves garlic, sliced; ½ teaspoon salt; ¼ teaspoon black pepper; 2 cups heavy cream; 1 cup Parmigiano, finely grated; 6 oz fontina, grated

This Fennel and Potato Au Gratin is my Italian-American take on the classic potato gratin. Thinly sliced russet potatoes and fresh fennel are layered with heavy cream, pancetta, Parmigiano Reggiano, and fontina for a rich, savory side dish with just a hint of sweetness from the caramelized fennel.

Look, it's not mashed potatoes, but I guess everything can't be my Garlic Parmesan Mashed Potatoes.

Spoonful of potato and fennel au gratin removed from the dish and placed on a plate.

Pair fennel and potato au gratin with classic roasts like Authentic Italian Porchetta or Italian Pork Roast!

A Quick Look at the Recipe

✅Recipe Name: Fennel and Potato Au Gratin
⏲️Ready in: 2 hours
👪Makes: 12 servings
📋Main ingredients: Fennel bulbs, Russet potatoes, Heavy Cream.
⭐Why You'll Love This Recipe: This is my Italian-American take on a traditional potato au gratin, so if you love au gratin and Italian flavors, this one is delicious.

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Why This Recipe

Fennel is one of those ingredients I don't think most people reach for the way they would an onion. But once it's slowly caramelized, its anise flavor mellows and it becomes subtly sweet, which makes it perfect for a rich dish like potato au gratin, or something simple, like Sausage and Fennel Pasta.

This fennel and potato au gratin takes everything I love about the classic au gratin: thinly sliced potatoes, plenty of cream, and a golden cheesy top. Then I add some Italian-American jazz, or as my dad would say, "doctor it up." The caramelized fennel brings sweetness, crispy pancetta adds a salty, savory bite, and Parmigiano and fontina give the gratin plenty of flavor without losing that creamy texture you expect.

Ingredient Notes and Substitutions

Ingredients for fennel potato au gratin.

Fennel- Slowly caramelizing fennel in rendered pancetta fat brings out its natural sweetness and mellows the signature anise to a more subtle flavor. It's what makes this potato gratin a little different from the classic version.
Russet Potatoes- Russet potatoes are my favorite option for fennel and potato au gratin because they are very starchy. As they bake, the starch helps thicken the cream and gives the gratin that rich, creamy texture.
Cheese- I love the combination of mild, melty fontina with the sharp and nutty Parmigiano. The fontina gives you the classic creamy, cheesy texture while the Parmigiano adds a little more depth and bite.
Pancetta- I love adding pancetta or other Italian pork to creamy potato dishes like this one because it adds a salty, savory flavor that keeps the dish from tasting like just another creamy potato dish. Rendering the pancetta first also gives us that flavorful fat to use for caramelizing the fennel.

*Please see the recipe card below for more information on the ingredients.

How to Make Fennel and Potato Au Gratin

Slicing potatoes for au gratin may be the one time I would bring out the mandolin, but for most home cooks who rarely use one, I think your safer bet is a sharp knife that you use often.

Step 1: Peel the potatoes. Thinly slice the potatoes to about ⅛-inch thick. Slice the fennel lengthwise, also about ⅛-inch thick.

Frying pancetta in a saucepan until golden brown.

Step 2: Add the pancetta to a large saucepan and set it over medium heat. Cook for 8-10 minutes, stirring occasionally, until golden brown and crisp. Transfer the pancetta to a plate, leaving the rendered fat in the pan.

Step 3: Add butter to the saucepan to melt. Stir in the fennel and season with ¼ teaspoon of salt. Sauté for 8-10 minutes, stirring occasionally, until the fennel begins to soften. Then stir in the garlic and combine.

Caramelizing fennel and garlic in a saucepan.

Step 4: Reduce the heat to medium-low and continue cooking for 25-35 minutes, stirring occasionally, until the fennel is soft, caramelized, and golden brown. Set aside on a plate to cool for 10 minutes.

Combining potatoes, cheese, and heavy cream in a large bowl.

Step 5: Meanwhile, combine the potatoes, heavy cream, ½ cup Parmigiano, 4 oz of fontina, ¼ teaspoon salt, and ¼ teaspoon pepper in a large bowl while cooking the fennel. Toss until the potatoes are evenly coated.

Combining pancetta, caramelized fennel and potato.

Step 6: Preheat the oven to 350 F. Add the caramelized fennel and pancetta to the potatoes and toss.

Pressing the potato mixture into a baking dish and topping with cheese.

Step 7: Grease the baking dish with butter. Transfer the potato mixture to the baking dish and spread evenly. Top with the remaining Parmigiano and fontina cheese.

Baking the dish covered with aluminum foil.

Step 8: Cover tightly with aluminum foil and bake for 1 hour.

Cover removed and baked until golden brown.

Step 9: Remove the foil and bake for an additional 20-30 minutes until the cheese is golden-brown and bubbling and a knife slides easily through the potatoes in the center of the dish.

Spooning out the fennel and potato au gratin.

Let the gratin rest for 10-15 minutes before serving. This is the perfect side dish to serve on the holidays with something like a Stuffed Turkey Breast, Garlic Parmesan Green Beans, or Maple Bacon Brussels Sprouts!

Pro-Tips

Preparing the potatoes and fennel. The potatoes and fennel need to be evenly cut so they all cook evenly. If the potatoes are all different thicknesses, the dish's texture will be a mix of too mushy and too al dente.
Rendering pancetta. When rendering pancetta, it's always best to start from a cold pan so that the fat begins to render first, and once the pan gets hot to fry, the meat of the pancetta will begin to become golden brown.
Caramelizing fennel. If you skip this step and just cook the fennel in the dish, although it may get soft enough, the flavor of the anise will be overwhelming and take over the dish. If you want to skip this step, try substituting a simple yellow onion.
Potatoes oxidizing. Once you cut the potatoes, they will begin oxidizing. Immediately put them in the mixture with the heavy cream to avoid that from happening.
Baking covered. The initial bake should be covered so that the inside gets cooked, but the cheese on top doesn't burn.
Resting. Resting fennel and potato au gratin isn't a suggestion just for temperature reasons. When the dish begins to cool, the starch will settle and the dish will set.

FAQs about Potato Au Gratin

How do you store and reheat fennel and potato au gratin?

This is one of those dishes where there is a lot of fat, so separation is almost guaranteed. The best way to store is in individual servings in aluminum foil or 2-cup containers. Then you can refrigerate for 3 days or freeze for up to 2 months. Reheat in the oven at 350 F for best results.

Can I make fennel and potato au gratin ahead of time?

Potatoes begin to oxidize as soon as you slice them open, so it's best made immediately. But once you add the potatoes to the cream mixture, the oxidation process will slow pretty dramatically. You can make the recipe up until the baking point and bake the following day. I would not recommend baking, refrigerating, and baking again because the texture will get mushy and there will be oil separation.

Do I need to use a mandoline?

You don't need to, but consistency in potato size is important. So, either use a very sharp knife or a mandoline to cut ⅛ inch pieces.

Serving Suggestions for Fennel and Potato Au Gratin

Casseroles or baked dishes like this are typically reserved for holidays, so they go best with roasts and large vegetable dishes! I'll guide you below with some ideas!