Wash and peel the potatoes: Start by rinsing the Yukon Gold potatoes under cold water. You can peel them or leave the skins on for added texture and nutrients. If you prefer a creamier bite, peeling is recommended., Slice the potatoes: Using a sharp knife and a cutting board, slice the potatoes into thin rounds, about ⅛-¼ inch thick. The goal is uniformity so they cook evenly., Boil potatoes: In a large pot, fill it with water and add a generous amount of salt. Bring it to a boil and carefully add the sliced potatoes., Cook until just tender: Boil them for about 8-10 minutes. You want them tender but not fully cooked since they will continue to cook in the oven., Drain and cool: After boiling, drain the potatoes in a colander and set aside to cool slightly. This prevents the potatoes from becoming mushy., Melt butter: In a medium saucepan, melt the unsalted butter over medium heat until bubbly., Add flour: Carefully add in the flour, whisking constantly for about 2-3 minutes to form a roux. This gives thickness to your cheese sauce., Slowly add milk: Gradually pour in the whole milk while continuously whisking to prevent lumps., Flavor it up: Add the garlic powder, onion powder, paprika, salt, and pepper. Let the mixture simmer for about 5-7 minutes, stirring occasionally until it thickens., Cheese it up: Reduce heat to low and add in the shredded cheddar and mozzarella cheeses, stirring until completely melted and creamy. Remove from heat., Preheat oven: Preheat your oven to 350°F (175°C)., Layer potatoes: Grease your 3-quart baking dish with a little olive oil. Add a layer of potatoes at the bottom, slightly overlapping each other., Pour cheese sauce: Spoon some cheese sauce over the first layer of potatoes. Sprinkle a tiny bit of salt and pepper on top to enhance flavor., Repeat layers: Add another layer of potatoes, followed by cheese sauce. Repeat this process until all ingredients are used, finishing with cheese sauce on top., Top your dish: Once layered, sprinkle the crumbled bacon and additional cheese on the top layer. This will create a lovely cheesy crust as it bakes., Bake: Cover the dish with aluminum foil and place it in the preheated oven for about 40 minutes. Then, remove the foil and bake for an additional 15-20 minutes until golden brown., Let it cool: Allow the loaded scalloped potatoes to cool for about 10 minutes before serving. This helps them set, making it easier to serve., Garnish: Just before serving, add a dollop of sour cream and a sprinkle of chopped green onions for a fresh finish.