Creamy Cheesy Onion and Potato Gratin

A rich and indulgent potato gratin with caramelized onions and a creamy, cheesy sauce, perfect for the holiday season.

By @foodie_lilly

Original recipe source

Cook time: 60 minutes

Servings: 6

Ingredients

• 2 onions finely sliced
• 1 knob salted butter
• 0 dried thyme to taste
• 5 large potatoes thinly sliced
• 0 salted butter for greasing
• 2.8 ounces salted butter for sauce
• 2 tablespoons plain flour heaped
• 13.5 ounces milk
• 7.05 ounces Aged Red Leicester cheese with roquito peppers
• 6 ounces Le Gruyère Aop Reserve
• 1 teaspoon whole grain mustard
• 0 salt to taste
• 0 black pepper to taste
• 0 grated cheese reserved for topping

Instructions

1. Preheat your oven to 350°F (180°C).
2. Finely slice the onions and heat a small knob of butter in a pan. Add the onions, season with salt and dried thyme, and let them cook until softened and caramelized.
3. Thinly slice the potatoes using a mandoline for consistency. Grease a baking dish with butter. Layer potatoes and caramelized onions in the dish.
4. For the white sauce, melt 80g of salted butter in a pan, then add 2 heaped tablespoons of plain flour. Cook for a minute, then gradually whisk in 400ml of milk to achieve a thick, silky consistency.
5. Add 200g of grated Aged Red Leicester cheese with roquito peppers and 170g of grated Le Gruyère Aop Reserve to the sauce. Stir in 1 teaspoon of whole grain mustard and season with salt and pepper.
6. Pour the cheese sauce over the layered potatoes and onions in the baking dish. Top with reserved cheese and bake in the oven for 45 minutes until bubbly and golden.