Fennel and Onion Gratin

cheesy fennel gratin in a cast iron skillet.

I have never been a fan of fennel. I don’t like licorice so, for me, it tracks that I don’t like fennel. But even at 29 years old, I want to continue to broaden and grow my palate. So, to try to like fennel, I created this fennel and onion gratin recipe. My thought was if anything can help me like fennel, it’s going to be cheese.

This fennel gratin recipe reminds me of French onion soup, which is my favorite kind of soup. So, in other words. I end up being a fan of fennel when it is smothered with cheese. Kinda like how you get kids to like broccoli by smothering it in cheese or hiding it in a broccoli and cheese soup. Cheese makes everything delicious.

The gratin likely gets its French onion soup vibes from the caramelization of the fennel and an onion together in the butter. When they are soft, I mix in the cheeses and half and half, then whack it in the oven really quick.

Be sure to save the tops (or fronds) of the fennel bulbs for a garnish for the top of the gratin. You likely won’t use all of the fronds, so after garnishing, I put them in my stock bag in the freezer. It’s a great addition to a homemade seafood stock.

I also managed to get nearly all of the ingredients for this dish from my Imperfect Foods box. Fennel, onions, butter, and both kinds of cheese all from Imperfect Foods.

fennel gratin in a cast iron skillet

Fennel and Onion Gratin

Course Side Dish


  • 2 fennel bulbs
  • 1 onion
  • 2 Tbsp butter
  • 1 c. grated gruyere
  • 1/4 c. grated parmesan
  • 1/4 c. half and half


  • Preheat the oven to 375 degrees.
  • Thinly slice the onion and the bulbs of the fennel. You'll chop the fronds and stalk off of the fennel, being left with just the bulb. You may want to take off the top layer of the bulb if it seems tough. Then slice it thinly like the onions.
  • Saute the onion and fennel in the butter until they are soft and slightly caramelized.
  • Mix in the paremesan, half and half, and the grueyere (exept for a few tablespoons of the gruyere). Then sprinkle on the few tablespoons of grueyere on top for a bubbly and golden top when you pull it out of the oven.
  • Place the whole thing in the oven and bake until the cheese is melted and golden.
  • Serve alongside your main course of steak, chicken, or hearty seafood.

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