Recipe: Ina Garten's Potato-Fennel Gratin | Williams Sonoma

Ingredients

• 2 fennel bulbs, stalks removed
• 1 yellow onion, halved and thinly sliced crosswise
• 2 Tbs. good olive oil
• 1 Tbs. unsalted butter
• 2 lb. (1 kg) russet potatoes, peeled (4 large potatoes)
• 2 cups (16 fl. oz./500 ml) plus 2 Tbs. heavy cream
• 2 1/2 cups (10 oz./310 g) grated Gruyère cheese
• Kosher salt and freshly ground pepper