Prepare the pork: Place the pork shoulder and sliced onion in a slow cooker. Pour the ginger beer over the pork. Cover and cook on low for 8-10 hours until the pork is tender and shreds easily.

Shred the pork: Once cooked, remove the pork from the slow cooker and shred it using two forks. Mix in 1 cup of BBQ sauce, adding more to taste. Set aside the shredded pork.

Cook the macaroni: Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to the package instructions until al dente. Drain and set aside.

Make the cheese sauce: In a large pot, melt the butter over medium heat. Sprinkle in the flour and whisk for about 1 minute to form a roux. Gradually pour in the warmed milk, whisking constantly to prevent lumps. Cook until the sauce thickens.

Combine macaroni and cheese sauce: Add the shredded cheddar cheese to the sauce, stirring until melted and smooth. Fold in the cooked macaroni until well coated with the cheese sauce.