Potato and Rutabaga Gratin | Saveur

Ingredients

• 4 tbsp. unsalted butter
• 2 tbsp. olive oil
• 4 cloves garlic, finely chopped
• 1 medium red onion, thinly sliced
• ¹⁄₄ cup flour
• 2 cups milk
• 1 cup heavy cream
• 1 lb. russet potatoes, peeled and very thinly sliced
• 1 lb. rutabagas, peeled and very thinly sliced
• 1 tbsp. minced thyme leaves
• 2 cups (about 4 oz.) grated Gruyére cheese
• osher salt and freshly ground black pepper, to taste