Preheat the oven to 400°.
Scrub russet and sweet potatoes. Pierce the potatoes at least several times with a fork. Place the potatoes in a foil lined 15x10x1 inch pan.
Bake until tender for about 60 to 70 minutes. Reduce the oven to 350°.
When cool enough to handle cut a third off of the top of each russet potato. Discard.
Scoop out the pulp leaving ½ inch thick shells. In a bowl mash the pulp adding ⅓ cup of sour cream, ¾ tsp salt, 2 tbsp chives, milk and cheese.
Cut a thin slice off of the top of each sweet potato. Discard the slice. Scoop out the pulp leaving ½ inch thick shells.
Mash the pulp with the remaining sour cream, salt, and chives.
Spoon russet potato mixture into half of each russet and sweet potato skin.
Spoon the sweet potato mixture into the other half. Return to the pans.
Bake until heated through about 15 to 20 minutes.