Fennel and Onion Gratin
By Ben MimsPublished on November 1, 2025
Time
1 hour
Yield
Serves 6 to 8
Ingredients
6 ounces Gruyère cheese, shredded (2 cups), divided1 cup panko bread crumbs 3 large fennel bulbs (2 pounds)1 large onion, sliced thin¾ cup water ¼ cup extra-virgin olive oil 1 teaspoon kosher salt 1 ½ cups heavy cream 3 tablespoons Dijon mustard 1 tablespoon all-purpose flour 1 ½ teaspoons pepper
Before You Begin
If desired, swap the Gruyère for an equally flavorful cheese such as Gouda or a sharp white cheddar. Serve the gratin as a side to roast meat or as a meal on its own with crusty bread and a salad.
Instructions
- Adjust oven rack to upper-middle position and heat oven to 425 degrees. Combine 1 cup Gruyère and 1 cup panko bread crumbs in bowl and rub between your fingers until coarse crumb is formed. Set aside.
- Coarsely chop 2 tablespoons fronds from 3 large fennel bulbs; set aside. Discard stalks from fennel. Halve fennel bulbs, core, and cut into 1½-inch wedges. Add fennel wedges to 12-inch nonstick skillet. Sprinkle 1 thinly sliced onion evenly over fennel. Add ¾ cup water, ¼ cup extra-virgin olive oil, and 1 teaspoon kosher salt and bring to simmer over medium-high heat. Cover and cook until fennel is translucent, shaking pan occasionally, 10 to 12 minutes.
- Remove lid and continue to cook, stirring occasionally, until all liquid has evaporated an vegetables are lightly browned, about 8 minutes.
- Transfer cooked vegetables to 2½-quart shallow baking dish and spread into even layer. In now-empty skillet, whisk together 1½ cups heavy cream, 3 tablespoons Dijon mustard, 1 tablespoon all-purpose flour, and 1½ teaspoons pepper and bring to simmer over medium heat. Stir in remaining 1 cup Gruyère and cook until just melted, about 1 minute. Remove from heat.
- Pour cheese sauce evenly over vegetables. Sprinkle panko mixture evenly over top. Bake until edges are bubbling and top is golden brown, 15 to 18 minutes. Top with reserved fennel fronds. Serve.
Time
1 hourYield
Serves 6 to 8Ingredients
6 ounces Gruyère cheese, shredded (2 cups), divided
1 cup panko bread crumbs
3 large fennel bulbs (2 pounds)
1 large onion, sliced thin
¾ cup water
¼ cup extra-virgin olive oil
1 teaspoon kosher salt
1 ½ cups heavy cream
3 tablespoons Dijon mustard
1 tablespoon all-purpose flour
1 ½ teaspoons pepper
Ingredients
6 ounces Gruyère cheese, shredded (2 cups), divided
1 cup panko bread crumbs
3 large fennel bulbs (2 pounds)
1 large onion, sliced thin
¾ cup water
¼ cup extra-virgin olive oil
1 teaspoon kosher salt
1 ½ cups heavy cream
3 tablespoons Dijon mustard
1 tablespoon all-purpose flour
1 ½ teaspoons pepper
Ingredients
6 ounces Gruyère cheese, shredded (2 cups), divided
1 cup panko bread crumbs
3 large fennel bulbs (2 pounds)
1 large onion, sliced thin
¾ cup water
¼ cup extra-virgin olive oil
1 teaspoon kosher salt
1 ½ cups heavy cream
3 tablespoons Dijon mustard
1 tablespoon all-purpose flour
1 ½ teaspoons pepper
Why This Recipe Works
Tender fennel and onions cloaked in lightly thickened cream and Gruyère add up to a simple yet sublime side. To ensure the proper texture, we parcooked the vegetables in a skillet and then transferred them to a baking dish. We used the same skillet to create a quick béchamel with heavy cream, a little flour, shredded Gruyère, and a generous amount of Dijon mustard to help temper the richness.
Before You Begin
If desired, swap the Gruyère for an equally flavorful cheese such as Gouda or a sharp white cheddar. Serve the gratin as a side to roast meat or as a meal on its own with crusty bread and a salad.
Instructions
- Adjust oven rack to upper-middle position and heat oven to 425 degrees. Combine 1 cup Gruyère and 1 cup panko bread crumbs in bowl and rub between your fingers until coarse crumb is formed. Set aside.
- Coarsely chop 2 tablespoons fronds from 3 large fennel bulbs; set aside. Discard stalks from fennel. Halve fennel bulbs, core, and cut into 1½-inch wedges. Add fennel wedges to 12-inch nonstick skillet. Sprinkle 1 thinly sliced onion evenly over fennel. Add ¾ cup water, ¼ cup extra-virgin olive oil, and 1 teaspoon kosher salt and bring to simmer over medium-high heat. Cover and cook until fennel is translucent, shaking pan occasionally, 10 to 12 minutes.
- Remove lid and continue to cook, stirring occasionally, until all liquid has evaporated an vegetables are lightly browned, about 8 minutes.
- Transfer cooked vegetables to 2½-quart shallow baking dish and spread into even layer. In now-empty skillet, whisk together 1½ cups heavy cream, 3 tablespoons Dijon mustard, 1 tablespoon all-purpose flour, and 1½ teaspoons pepper and bring to simmer over medium heat. Stir in remaining 1 cup Gruyère and cook until just melted, about 1 minute. Remove from heat.
- Pour cheese sauce evenly over vegetables. Sprinkle panko mixture evenly over top. Bake until edges are bubbling and top is golden brown, 15 to 18 minutes. Top with reserved fennel fronds. Serve.
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