Preheat your oven to 400°F (200°C). Thoroughly scrub the six large Russet potatoes and dry them completely.

Rub the outside of each potato with the 2 tablespoons of olive oil or vegetable shortening, then sprinkle them evenly with the 1 teaspoon of Kosher salt. Pierce each potato deeply four to five times using a sharp fork.

Place the prepared potatoes directly on the oven rack (or a foil-lined sheet). Bake for 50 to 75 minutes, or until the potatoes are tender when squeezed. Carefully remove the potatoes and let them cool on a wire rack for about 10 to 15 minutes, until they are cool enough to handle.

Reduce the oven temperature to 350°F (175°C). Slice off the top 1/4 inch of each potato lengthwise. Carefully scoop out the fluffy potato flesh into a large mixing bowl, leaving a sturdy 1/4 inch border of potato attached to the skin to maintain the shell structure. Set the empty shells aside on a baking sheet.

Add the 4 tablespoons of softened butter, the 1/2 cup of milk or cream, and the 1/2 cup of sour cream to the scooped potato flesh. Beat or mix the contents until the mixture is light, fluffy, and smooth. Be careful not to overmix.

Fold in 1 cup of the shredded sharp cheddar cheese, the 1 teaspoon of Kosher salt, the 1/2 teaspoon of black pepper, and half (1/4 cup) of the chopped fresh chives or green onions. Taste the filling and adjust seasoning if needed.

Spoon the potato mixture generously back into the six empty potato shells, mounding the filling high above the shell rim.

Evenly sprinkle the remaining 1/2 cup of shredded sharp cheddar cheese over the top of the filled potatoes. If desired, sprinkle a small pinch of paprika over the cheese.

Bake in the preheated 350°F (175°C) oven for 15 to 25 minutes, or until the filling is heated through and the cheese is melted, bubbly, and lightly golden brown. Garnish immediately before serving hot with the remaining fresh chives or green onions.