Fennel + Onion Gratin

This crispy, cheesy fennel and onion gratin is perfect for the holidays and chilly winter months. The onions and fennel get cooked down in butter to become super sweet, tender and mellow. They get mixed with sharp Pecorino Romano cheese, fresh thyme and a splash of cream, then get baked with an ultra crispy breadcrumb topping. It's an easy, make-ahead side that's lovely with steak, chicken, turkey, pork or fish. 

Why this recipe works

• Inspired by the creamed peal onions that often show up on the Thanksgiving table, this is a more modern take that tastes sooo much better.
• Onions and fennel get cooked down to become super sweet, tender and mellow. Even self proclaimed fennel haters will fall in love!
• Pecorino Romano cheese adds a sharp, salty flavor that pairs perfectly with the sweet fennel and onions.
• Toasting Panko breadcrumbs in butter before baking ensures a perfectly light and crisp topping with no soggy bits.
• Can be made entirely in advance for easy entertaining or bringing to a potluck.

Essential Ingredients

• Onions - I love making this with sweet onions such as Vidalia, but regular yellow onions will still work great.
• Pecorino Romano Cheese - Locatelli brand is the gold standard - use it if you can find it. You can substitute parmesan, however it will have a more mild flavor.
• Panko Breadcrumbs - These light, airy Japanese breadcrumbs make the best topping. Substitute homemade bread crumbs made from torn stale bread if you can't find them.

Step by Step Instructions

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1. Use a mandolin or sharp knife to thinly slice the onions and fennel (use only the white bulb of the fennel and avoid the green stems). If the fennel is very large, remove the core with a knife before slicing, as it can be tough.

2. Melt 2 tablespoons of butter in a large saucepan over medium heat, then add the fennel and give it a stir. Cover and let cook for about 10 minutes, stirring occasionally.

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3. Add the onions, stir, then cover and let cook until tender, stirring occasionally, about 15 minutes.

4. While the fennel and onions cook, melt the remaining two tablespoons of butter in a medium saute pan. Add the Panko breadcrumbs and stir.

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5. Continue stirring the Panko until golden and toasted, about 3 minutes. Set aside to cool.

6. Once the fennel and onions are tender, add the heavy cream and fresh thyme, then season with salt and pepper to taste. Cook uncovered until the cream reduces by about ⅓, about 5 minutes.

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7. Remove the pan from the heat and stir in the Pecorino Romano cheese.

8. Butter the inside of an 8-9 inch cast iron skillet or casserole dish, then pour in the mixture and smooth out the top. Sprinkle with more Pecorino Romano cheese, then the toasted breadcrumbs. If making the recipe ahead, let it cool, wrap tightly and refrigerate for up to 3 days before baking.

9. Bake in a preheated 425 degrees F oven for about 20 minutes or until it's bubbling around the edges. If baking from the refrigerator, lower the oven temp to 375 and bake for 30 minutes total.

Tips for Success

• Use a mandolin slicer for best results. This will result in uniformly thick slices of onion and fennel which will have a better finished texture. Nervous about using one? A cut proof glove is your best friend.
• If the top is browning too quickly while it bakes, tent the pan with foil to slow the process.
• This recipe can be made (before baking) up to 3 days ahead. Wrap tightly and store in the refrigerator, then bake at 375 degrees F for about 30 minutes. I do not recommend freezing.

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