1Heat oven to 375°F. Gently scrub potatoes, but do not peel. Pierce potatoes several times with fork. Bake 1 hour to 1 hour 15 minutes or until potatoes are tender when pierced in center with fork. Let stand until cool enough to handle.
2Cut each potato lengthwise in half; scoop out insides into medium bowl, leaving a thin shell. Add milk to potatoes; mash with potato masher or electric mixer until no lumps remain (amount of milk needed will vary depending on type of potato used). Stir in pesto, tomatoes, olives and 1/2 cup cheese. Fill potato shells with mashed potato mixture. Place on ungreased cookie sheet.
3Bake about 20 minutes or until hot. Sprinkle with basil and additional cheese.