Preheat oven to 425°F. Tear off 4 squares of heavy-duty aluminum foil, each large enough to wrap one potato.

Scrub potatoes thoroughly under cold water and dry completely with paper towels. Moisture on the skin will steam off rather than allow the bacon fat to adhere properly.

Working with one potato at a time, rub 1 tablespoon of bacon fat all over the potato, covering every surface. The fat should coat the skin in a thin, even layer - not pooling, but fully covered.

Sprinkle 1 teaspoon of kosher salt over each fat-coated potato, pressing gently to adhere. The salt should be visible and fairly generous - this is intentional.

Place each potato on a square of foil and wrap tightly, sealing all edges. This traps bacon fat against the skin throughout baking, steaming the interior to a fluffy, cloud-like texture.

Place wrapped potatoes on the center oven rack. Bake for 60 to 70 minutes, until a knife inserted through the foil and into the center meets no resistance.

While the potatoes are baking, cook bacon until crispy. Drain on paper towels, then cut or crumble into pieces.

Remove the baked potatoes from the oven. Carefully open the foil and slit the potato lengthwise across the top. Squeeze the ends toward the center to push the interior up and open.

For the loaded version: Work a tablespoon of soft (not cold) butter into the hot potato immediately. The butter should be at room temperature so it melts into the flesh rather than sitting on top. Add cheddar cheese while the potato is still at peak temperature so it melts completely. Top with sour cream, crumbled bacon, and fresh chives. Serve immediately.