Preheat your oven to 400°F (200°C). Wash the potatoes thoroughly, scrubbing the skin clean. Pat the potatoes completely dry.

Rub each potato lightly with olive oil and prick them several times across the surface using a fork or sharp knife. Sprinkle the skins generously with coarse salt.

Place the potatoes directly on the oven rack. Bake for 60 to 75 minutes, or until the skin is crispy and the interior is fork-tender. Remove the potatoes from the oven and let them cool on a wire rack for about 10 to 15 minutes, or until they are cool enough to handle safely. Reduce the oven temperature to 350°F (175°C).

Using a sharp knife, carefully slice the top third lengthwise off each potato, or slice the potato lengthwise down the middle. Gently scoop the hot potato flesh out into a large mixing bowl, taking care to leave a sturdy, 1/4-inch thick shell intact. Set the potato skins aside.

Add the softened butter, sour cream, and heavy cream (or milk) to the scooped potato flesh. Use a sturdy fork or a hand mixer to mash the mixture until it is smooth and creamy. Do not overmix, as this can make the potatoes gummy.

Add 1 cup of the shredded cheddar cheese, the kosher salt, black pepper, and the optional bacon and chives to the filling mixture. Fold gently until everything is evenly combined. Taste the mixture and adjust seasonings as desired.

Spoon the filling mixture back into the empty potato shells. Heap the filling slightly above the edge of the skin, smoothing the top with the back of a spoon.

Sprinkle the remaining 1/2 cup of shredded cheddar cheese evenly over the top of the filled potatoes. Place the filled potatoes on a baking sheet.

Bake for 15 to 20 minutes at 350°F (175°C), or until the potatoes are heated through and the cheese topping is melted, bubbly, and lightly golden brown. Garnish with extra fresh chives or a dollop of sour cream if desired. Serve immediately.