Fennel and Onion Gratin

fennel onion gratin in a cast iron skillet with spoon and scoop taken out

Fennel and Onion Gratin

This simple recipe for fennel and onion gratin is perfect for the holidays. The onions and fennel cook down to be super sweet with an ultra crispy top.

5 from 1 vote

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Course: Side Dish

Cuisine: American

Keyword: cheesy, easy side dish, fennel, gratin, onion

Prep Time: 10

Cook Time: 50

Total Time: 1

Servings: servings

Calories: 270kcal

Author: Nicole Gaffney (ColeyCooks.com)

Ingredients

4 tablespoons butter divided, plus more for greasing the dish
1 large or 2 smaller fennel bulbs thinly sliced (if very large, remove the core)*
2 medium-large sweet onions peeled, halved and thinly sliced
1 teaspoon salt plus more to taste
freshly cracked black pepper to taste
1 teaspoon fresh thyme leaves sub ¼ teaspoon dried
¾ cup heavy cream
1 ¼ cups finely grated pecorino Romano cheese
1 cup panko breadcrumbs

Instructions

Preheat the oven to 425 degrees F.
Melt two tablespoons of butter in a large saucepan over medium heat. Add the fennel, season with salt, stir, then cover and let cook for about 10 minutes.
Add the onions, stir, cover, and cook, stirring occasionally, until tender, about 15 minutes.
while the fennel and onion cook, melt the remaining two tablespoons of butter in a medium saute pan.
Add in the panko breadcrumbs and stir around until they're golden and toasted. Set aside to cool.
When the onions and fennel are tender, add the heavy cream and thyme, then season with salt and pepper.
Cook uncovered for a few minutes until the cream has reduced by about ⅓, then remove from the heat and stir in 1 cup of Pecorino Romano cheese.
Butter the inside of an 8-9 inch casserole dish or cast iron skillet, then add the fennel mixture and smooth out the top.
Sprinkle with remaining Pecorino Romano cheese and then the toasted breadcrumbs.
Bake for about 20 minutes or until its bubbling and golden brown on top.

Video

Notes

*For best results, use a mandolin slicer to cut the fennel and onions
If making ahead, assemble completely, but do not bake. Cover and store in the refrigerator up to 3 days ahead. Bake at 375 degrees F for about 30 minutes until its bubbling around the sides. If the top starts to get too brown, tent it with foil.

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