1. 1. Prepare the Potatoes: Preheat your oven to 400 F (200 C). Scrub the russet potatoes clean under running water, then pat them dry. Pierce each potato several times with a fork. Rub a little olive oil over the skin of each potato, then sprinkle with salt. Place them directly on the oven rack and bake for 45-60 minutes, or until they are tender when squeezed and easily pierced with a fork.

2. 2. Make the Buffalo Chicken Filling: While the potatoes are baking, combine the shredded cooked chicken, buffalo wing sauce, ranch dressing, and softened cream cheese in a medium saucepan. Heat over medium-low heat, stirring frequently, until the cream cheese is fully melted and the mixture is well combined and heated through. This should take about 5-7 minutes. Stir in 1 cup of shredded cheddar cheese and the Monterey Jack cheese until melted and creamy. Remove from heat.

3. 3. Scoop Out the Potato Flesh: Once the potatoes are baked and cool enough to handle (about 5 minutes), carefully slice each potato lengthwise down the middle, being careful not to cut all the way through the bottom skin. Use a spoon to scoop out the fluffy potato flesh into a large bowl, leaving a thin border of potato attached to the skin to maintain its structure.

4. 4. Mash and Season the Potato Flesh: To the scooped-out potato flesh, add the melted butter, milk, and salt and pepper to taste. Mash everything together until smooth and creamy. You can leave a few small lumps if you prefer a more rustic texture.

5. 5. Combine Filling and Potato: Gently fold about half of the mashed potato mixture into the buffalo chicken filling. This will make the filling extra creamy and help it hold together better when stuffed.

6. 6. Stuff the Potato Shells: Spoon the remaining mashed potato mixture back into the potato skins, creating a base. Then, generously spoon the buffalo chicken mixture over the mashed potato in each potato shell, mounding it high.

7. 7. Final Bake and Melt: Sprinkle extra shredded cheddar cheese over the top of each stuffed potato. Return the potatoes to the oven for another 5-10 minutes, or until the cheese is melted and bubbly and the filling is thoroughly heated through.

8. 8. Garnish and Serve: Carefully remove the potatoes from the oven. Garnish with chopped green onions, a drizzle of extra ranch or blue cheese dressing, and a side of celery sticks if desired. Serve immediately and enjoy!