Ingredients
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2 medium fennel bulbs (about 1 1/2 lbs)
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2 tbsp olive oil, plus more for greasing
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1 cup diced onions
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3 tbsp butter, cut up
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2 cups half & half
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2 lbs russet potatoes
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1 1/2 cups shredded Gruyère cheese (about 7 oz), divided
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Cooking spray
Steps
1
Preheat oven to 400°F. Grease a 2½-qt baking dish with some oil.
2
Cut stalks off the fennel and quarter bulbs lengthwise. Cut out and discard cores and very thinly slice fennel. In a 10-inch skillet, heat the oil on medium. Add the onions and fennel. Season with salt. Cook 8–10 min., until tender, stirring occasionally. Cool slightly.
3
Meanwhile, to a medium, microwave-safe bowl, add the butter. Cover with vented plastic and microwave 1–2 min., until melted. Whisk in the half & half until smooth. Season with salt and pepper.
4
Peel and very thinly slice the potatoes. In prepared dish, arrange ⅓ of potato slices in even layer. Top with ⅓ of fennel mixture. Pour ⅓ of half & half mixture on top. Sprinkle with ½ cup Gruyère. Repeat layering twice more.
5
Coat a piece of foil with the cooking spray and cover the gratin. Bake 30 min. Remove foil and continue baking 20–25 min., until potatoes are tender when pierced with a knife and top is golden brown. Let stand 15 min. before serving.
Tips
Use a mandoline or food processor with slicing attachment to slice potatoes quickly and evenly.
