01 - Preheat your oven to 400°F (200°C). Thoroughly scrub the russet potatoes and pat them completely dry. Pierce each potato several times with a fork. Rub the potatoes with olive oil, kosher salt, and black pepper. Place the seasoned potatoes directly onto the oven rack and bake for 45–50 minutes, or until they are tender when pierced. Allow them to cool slightly.
02 - While the potatoes are baking, cook the elbow macaroni in salted boiling water according to the package directions until al dente. Drain the macaroni thoroughly and set aside.
03 - In a medium saucepan, melt the unsalted butter over medium heat. Whisk in the all-purpose flour and cook for 1 minute to form a paste. Gradually add the whole milk while whisking constantly until the mixture thickens into a smooth sauce, approximately 2–3 minutes.
04 - Remove the saucepan from the heat. Stir in 1 cup of the shredded sharp cheddar cheese until melted. Incorporate the garlic powder and mustard powder. Season the mixture with salt and pepper to your preference. Gently fold in the cooked elbow macaroni.
05 - Once the potatoes are cool enough to handle, carefully cut each potato in half lengthwise. Gently scoop out most of the cooked potato flesh, ensuring a 1/4-inch shell remains. Reserve the scooped potato flesh for another culinary use.
06 - Arrange the hollowed potato skins on a baking sheet. Generously fill each potato skin with the prepared mac and cheese mixture. Sprinkle the remaining 1/2 cup of shredded cheddar cheese over the top of each filled skin.
07 - Return the baking sheet to the preheated oven and bake for an additional 10–12 minutes, or until the cheese on top is completely melted and bubbly. Garnish the finished potato skins with chopped fresh chives and crumbled bacon, if using. Serve hot.