Bake Potatoes: Wash and dry the potatoes, then prick the outsides of the potatoes a few times with a knife or fork. Rub them with olive oil and season with salt and pepper. Bake potatoes at 400 for about 1 hour, or until fork tender. Remove from oven and allow to rest until cool enough to handle.
Remove potato flesh: Cut the top, lengthwise of each potato off and scoop out the flesh into a mixing bowl, leaving 1/4 inch layer of potato flesh and skin, and the rest hollowed out.
Season mashed potatoes: Add butter, salt and pepper, chives, sour cream, garlic powder, chicken bouillon, and milk. Mash with a potato masher and then mix with beaters until smooth (but don’t over-mix them or they will be gluey instead of light and fluffy.) Add more milk, if needed—it’s better if the filling is on the softer side because the potato mixture will thicken up as it cooks again in the oven.
Bake: Top with shredded cheese and bake at 350 degrees F for 15 minutes or until the cheese is bubbly.
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Notes
Tip: Don't over mix the potato filling. Over-mixing causes mashed potatoes to become gluey instead of light and fluffy.To Make Ahead: Prepare potatoes completely, without baking them the second time. Place them on a large sheet pan, lightly cover with plastic wrap and refrigerate up to one day, until ready to bake. If making them ahead, I suggest adding a little extra milk to the mashed potato filling so they are extra soft before sitting in the fridge for several hours.To Freeze: Flash freeze them on a baking tray until they're solid (about 30 minutes), then store in a freezer-safe bag of container for up to 3 months. Thaw completely in the fridge before warming in the oven. (I don't think frozen and then baked Twice Baked Potatoes have the same quality as when freshly made, so I would only use this method if it was really necessary).