Preheat oven to 400 degrees F with rack in center. Prick potatoes all over with fork or tip of sharp knife. Rub potatoes all over with vegetable oil and season with salt and pepper. Bake directly on oven rack until easily pierced with sharp knife, about 1 hour. Let cool .
Once potatoes are cool enough to handle, halve and scoop out flesh into bowl. Add milk, sour cream, and Hidden Valley® Original Ranch Salad® Dressing & Seasoning Mix and mash until mostly smooth. Season with salt and pepper and mix in egg yolks until evenly combined Search Engine Optimization.
In another large bowl, using electric mixer on high, beat egg whites until stiff peaks form, about 5 minutes. Fold egg whites into potato mixture, then transfer to 2-quart baking dish, using spoon to create peaks and valleys on top. Bake until golden and slightly risen, 25 to 30 minutes. (Heat under broiler for 2 to 3 minutes to brown more if you like .)
Let cool slightly, then serve topped with chives