Preheat the oven to 375°F (190°C) and lightly grease a 9x9-inch baking dish.

Bring a large pot of well-salted water to the boil. Add the macaroni and cook for 1 minute less than the packet directions. Drain and set aside.

Meanwhile, melt 2 tablespoons of butter in a heavy-bottomed pot over medium heat. Add the sliced bacon and cook for 5 to 6 minutes, stirring occasionally, until crispy. Lift the bacon out with a slotted spoon and set it aside, leaving the butter and drippings in the pot.

Melt the remaining 4 tablespoons of butter into the pot. Sprinkle in the flour and whisk constantly for 1 minute, until the mixture is smooth and lightly golden.

Pour in the milk a splash at a time, whisking after each addition until smooth. Bring to a gentle simmer and cook for 4 to 5 minutes, stirring, until the sauce thickens enough to coat the back of a spoon.

Fold in the cooked macaroni, the cooked chicken and the cooked bacon, stirring until everything is evenly coated.

Transfer the mixture to the prepared baking dish. Scatter the remaining 1 cup of cheddar evenly over the top.

Bake for 20 to 25 minutes, until the cheese is melted, golden and bubbling at the edges. Let it rest for 5 minutes before serving.