Begin by peeling and dicing 1.5 kg of baking potatoes into equal pieces. Place them in a large pot, cover with cold, salted water, and bring to a boil over medium-high heat. Cook for about 15-20 minutes until the potatoes are knife-tender; they should easily break apart. Once cooked, drain and let sit for 1 minute to dry slightly.

Return the drained potatoes to the pot and add 6 tablespoons of room-temperature butter and 160 ml of warmed cream. Mash them together until smooth and creamy, ensuring no lumps remain. Stir in 150 g of grated cheddar cheese and season with salt and 1/4 teaspoon of black pepper, mixing well until the cheese is melted and fully incorporated.

While you prepare the gratin topping, set your oven to preheat at 200°C (400°F). This temperature is crucial for achieving that perfect golden crust on the top layer of your cheesy mashed potato gratin.

Take 750 g of baking potatoes and peel them before slicing them into thin half-moons. In a mixing bowl, melt 2 tablespoons of butter and combine it with 1 minced garlic clove, a pinch of salt, and additional black pepper. Toss the sliced potatoes in this mixture along with half of the 40 g of diced Parmesan, ensuring all slices are evenly coated for flavor.

In a baking dish, spoon the creamy mashed potatoes and spread them out evenly to create a smooth layer. Next, layer the garlic buttered potato slices on top of the mash, stacking them at a slight angle for an appealing presentation. Press down gently to ensure the layers meld together.

Cover the baking dish with aluminum foil and place it in the preheated oven. Bake for 20 minutes to allow the flavors to meld. After this, carefully remove the foil and sprinkle the remaining Parmesan evenly over the top.

Return to the oven and bake uncovered for an additional 40 minutes, or until the top is golden brown and crispy.

Once out of the oven, let the cheesy mashed potato gratin rest for 15-20 minutes. Just before serving, garnish with freshly chopped chives for a pop of color and a fresh touch.