In a large non-stick skillet over medium heat, brown the onion in 1 tbsp of the butter. Season with salt and pepper. Transfer to a large bowl. Let cool.
In a small bowl, combine the brown sugar and spices. Reserve 1 tbsp of the mixture for the pan sauce.
Add the ground beef and pork, breadcrumbs, milk, egg and spice mix to the onions. Season with salt. Mix thoroughly.
Shape each meatball with about 1 tbsp of the mixture. Set aside on a plate. You should end up with approximately 50 meatballs.
In the same non-stick skillet over medium-high heat, brown the meatballs, half at a time, in ¼ cup (55 g) of the butter until nicely browned on all sides. Set aside on another plate.
6. Sprinkle the flour over the hot fat in the skillet and cook for 2 minutes, stirring constantly until the mixture turns golden brown. Whisk in the broth and reserved spices and bring to a boil. Add the meatballs. Cover and gently simmer for about 5 minutes or until the meatballs are cooked and the sauce thickens. Keep warm.
In a bowl, dissolve the cornstarch in the milk.
In a small pot over medium heat, melt the butter with the flour, stirring with a whisk. Cook for 1 minute. Add the milk mixture and bring to a boil, whisking continuously. Add the cheese and stir until melted. Adjust the seasoning. If desired, add a few drops of food colouring to give the sauce an even deeper orange hue.
To serve, place the meatballs in bowls. Drizzle with the cheese sauce.