Preheat the oven to 425°F and line a baking sheet with parchment paper.

Use a fork to poke a few holes in the potatoes. Place on the baking sheet and rub with olive oil. Bake for 60 to 70 minutes, or until easily pierced with a fork.

Remove the potatoes from the oven and allow to cool slightly. When they are cool enough to handle, slice in half lengthwise. Use a spoon to scoop out the flesh from the centers of the potato halves, leaving a ¼-inch border around the edges.

Transfer the scooped-out flesh to a large bowl and mash with the milk, sour cream, butter, garlic, salt, and pepper until smooth and creamy.

Arrange the potato skins cut side up on the baking sheet. Sprinkle with salt, then fill with the creamy potato mixture. Top with the cheese and bake for 15 to 25 minutes, or until the cheese is melted and beginning to brown.

Remove from the oven and garnish with the green onions. Season to taste and serve.