Ingredients

• 2 1/4 cups whole milk
• 2 tablespoons unsalted butter
• 1 small Spanish onion, finely chopped
• 2 tablespoons all-purpose flour
• 1/4 teaspoon kosher salt
• Pinch cayenne pepper
• 1/2 pound crumbled blue cheese
• Homemade Potato Chips, recipe follows, or good-quality store-bought potato chips
• 6 large Idaho potatoes, peeled and sliced lengthwise into 1/8-inch thick slices on a mandoline
• 2 quarts peanut oil
• Salt

Instructions

1. Watch how to make this recipe.
2. Place the milk in a small saucepan and bring to a simmer over low heat. Heat the butter in a medium saucepan over medium heat. Add the onion and cook until soft. Stir in the flour and cook for 1 minute. Slowly whisk in the warm milk, and continue whisking until thickened. Season with salt and cayenne pepper. Continue cooking for 5 minutes, whisking occasionally. Remove from the heat and stir in the cheese. If the sauce is too thick, thin it with a little extra milk. Serve sauce warm with potato chips for dipping.
3. Place the potato slices on a baking sheet between layers of paper towels to make sure they are very dry before frying.
4. Heat oil in a large, heavy saucepan until the temperature of the oil reaches 400 degrees F on a deep-fat thermometer. Fry the potatoes in small batches until golden brown on both sides, turning once. Remove with a slotted spoon and place on a brown paper bag or another baking sheet lined with paper towels to drain. Season with salt immediately. Serve hot with the blue cheese dipping sauce.