Preheat the oven to 425 degrees. Begin by piercing the potatoes with a fork or a knife then add the potatoes to an over rack centered in the middle of the oven. Bake for 1 hour and 20 minutes or until potatoes are tender and can be easily squeezed. That means they are completely cooked through.
Next allow the potatoes to cool down for 20 minutes.
Lower the temperature of the oven to 350 degrees.
With a sharp knife, cut each potato in half lengthwise. Scrape out the flesh inside of the potatoes into a mixing bowl, being careful not to tear the outside jacket shell of the potatoes.
Add the butter, heavy cream, sour cream, chives, half of the cheddar cheese, parmesan cheese, eggs, salt and pepper to the potato flesh that was scraped into the bowl. Mash everything together until combined.
Spoon the potato mixture back into the potato jackets. Add the filled potatoes to a baking sheet and sprinkle on the remaining cheese.
Bake for 30-35 minutes at 350 until the cheese is completely melted and potatoes are tender and heated. Serve immediately.
REHEATING FROM FROZENWhen ready to eat, thaw the potatoes for 24 hours in the fridge. Unwrap the potatoes, top with extra cheese (because why not), and place them on a lightly greased baking sheet. Proceed with one of the reheating methods below. MICROWAVE: Place the thawed potatoes on a microwave-safe plate. Heat on high power, uncovered, for 2-3 minutes or until heated through. OVEN: Bake 350 degrees until heated through, about 20-25 minutes. Alternatively, you can bake the potatoes from frozen for about 60-70 minutes.