Place potatoes on a foil lined baking sheet and bake for 50 – 60 minutes or until potatoes are fork tender. Set aside to cool. Increase temperature of oven to 400 degrees.
Cook bacon over medium heat in a large skillet until browned and crispy. Place cooked bacon on a plate lined with paper towels. Wipe pan with paper towel leaving about 1 teaspoon of drippings. Add spinach and cook until wilted (about 3-5 minutes).
Cut cooled potatoes in half lengthwise. Scoop out most of the flesh into a bowl, leaving about ¼ inch border inside the skin.
Set a baking rack on the foil-lined baking sheet and place the sweet potatoes on it skin-side up. Brush each skin with olive oil. Bake for 25-30 minutes or until skins are slightly browned. Remove from the oven and allow to cool slightly.
Combine 11/2 cups sweet potato flesh, the wilted spinach, half of the cooked bacon, salt, and pepper in a large bowl. Mix to combine. Gently stir in 11/2 cups cheese.
Fill each sweet potato skin with the sweet potato mixture and sprinkle evenly with the remaining bacon and cheese. Bake for 10 minutes or until the cheese is melted then broil for 2 to 3 minutes until the tops are slightly brown.
Top each skin with the rest of the cheese and bacon. Sprinkle with chopped chives and serve with sour cream for dipping.