Potato Casserole with Caramelized Onions

Bahan-bahan (12 porsi)

• 3/4 cup (1½ sticks) butter, (divided)
• 1/4 cup olive oil
• 6 large sweet onions, (sliced thinly)
• 1 tablespoon granulated white sugar
• 4 pounds baking potatoes, (peeled and cubed)
• 4 cups chicken broth
• 1 cup whipping cream
• 1 cup sour cream
• 4 large eggs, (beaten)
• 1/2 teaspoon salt