Peel and dice. Peel all of the potatoes and dice into roughly 1-inch cubes for boiling.
Boil. Bring a large pot of salted water to a boil. Carefully add the potatoes and cook for 8 to 12 minutes or until the potatoes are easily pierced with a fork. When checking the done-ness of the potatoes check both the russets and the Yukon gold since the Yukon gold are a little denser.
Blend or mash. Drain the cooked potatoes well and transfer to a standing mixer. Beat on low speed with the paddle attachment until all the potatoes are smooth, about 2 minutes. If you don't have a standing mixer, transfer the potatoes to a mixing bowl and use a traditional potato masher
to press the potatoes until there are little to no clumps.
Make it creamy. In a saucepan, melt the butter. Once the butter is melted, add the milk and heat just until warmed. Transfer to the potatoes and mix. The potatoes may seem a little loose at first but will firm up as the ingredients combine. Lastly, mix in the softened creamed cheese on low speed or by hand until fully incorporated.
Season. Taste the potatoes and season generously with salt and a little black pepper, about 1 teaspoon salt, and ¼ teaspoon black pepper. Taste again to see if more seasoning is needed.
Serve. Serve the mashed potatoes immediately or hold them in a crockpot or dutch oven until you're ready to serve. Because these potatoes are super creamy and light, they can be reheated before serving without becoming dry or heavy.