1. Bake whole potatoes in preheated 450*F. oven for about one hour; take potatoes out and reduce oven temperature to 350*F.
2. Let potatoes rest for 5 minutes, then cut in half lengthwise and scoop out potato flesh into a large bowl. Reserve potato jackets.
3. Add butter, sour cream, milk, salt, pepper, and cheese to potato in bowl, and whip until creamy with an electric hand mixer.
4. Taste and adjust seasoning with additional salt and pepper.
5. Gently stir in scallions and avocado pieces. Spoon mixture into halved potato jackets, and bake in 350*F. oven for 20 minutes.
6. Top each potato half with a heaping spoonful of guacamole to serve. Enjoy!