- Bake whole potatoes in preheated 450-degree oven for one hour; remove potatoes and reduce oven temperature to 350 °F.
- Let potatoes rest for 5 minutes, then cut in half lengthwise and scoop out potato flesh into large bowl. Reserve potato jackets.
- Add butter, sour cream, milk, salt, pepper, and cheese to potato in bowl, and whip until creamy with electric hand mixer.
- Taste and adjust seasoning with additional salt and pepper.
- Gently stir in chives and avocado pieces. Spoon mixture into halved potato jackets, and bake in 350 °F oven for 20 minutes.
- Top each with heaping spoonful of guacamole to serve.