1. Preheat your oven to 400°F (200°C), making sure it's nice and hot for our potato gratin.

2. Peel the potatoes and slice them into thin rounds – you want them to be nice and delicate for this dish.

3. In a greased baking dish, create a layer of potatoes. Don't worry too much about perfection here – we're going for a rustic, homemade feel.

4. Sprinkle some aged cheddar cheese over the potatoes. This is a key ingredient in our dish, so be generous with it.

5. Keep repeating the layering process – potatoes, cheese, potatoes, cheese – until you've used up all your ingredients, finishing with a layer of cheese on top. You want that golden-brown crust to form in the oven.

6. Dot the top of the gratin with butter. This will add a richness and depth to our dish that's hard to resist.

7. Pop the gratin in the preheated oven and bake for about 45 minutes, or until the potatoes are tender and the top is a gorgeous golden brown.

8. Once it's done, remove the gratin from the oven and sprinkle some chopped red onion, parsley, and chives on top. This adds a fresh, oniony flavor to the dish that complements the cheese and potatoes perfectly.