Preheat the oven to 350°F (177°C). Spray a 9x13 baking dish with nonstick cooking spray and set aside.
Add the cubed sweet potatoes to a large pot/saucepan, cover the sweet potatoes with water, and place over medium to high heat. Bring to a boil, reduce heat to medium, and allow the potatoes to cook for 10 to 15 minutes or until you can easily pierce them with a fork. Drain the potatoes and set aside to cool for 10 to 15 minutes.
Place the sweet potatoes in a large mixing bowl and mash well. You may also use an electric mixer to help make them smoother. Add the brown sugar, milk, butter, vanilla, cinnamon, salt, and eggs and mix until fully combined. I prefer to use an electric mixer for this step, but you may also do this by hand.
Scoop the sweet potato mixture into the prepared baking dish and spread it around into one even layer. Set aside.