Preheat oven to 385 degrees F (195 degrees C).

Fry the bacon in a cast iron skillet over medium heat. Flip the bacon frequently until most of the fat has burned off. Turn off the heat. This should take between 5 to 10 minutes. Line a plate with a paper towel, and place the cooked bacon on the lined plate.

Add the rosemary into the bacon fat, and give everything a quick stir to infuse the rosemary flavor.

Rinse the fingerling potatoes and dry them completely. Slice them in half. If the potato is fairly large, cut it into quarters. Place them cut side down in the skillet. Spoon and drizzle any extra bacon fat on top of the potatoes. Sprinkle the garlic and salt on top.

Bake for 25 minutes. You can flip some of the potatoes if you want more sides to be browned. Then, turn the heat up to 400 degrees F (205 degrees C) and bake for another 5 to 7 minutes. The potatoes will be done when they're easily pierced with a fork. While the potatoes are baking, rip off any extra fat from the cooked bacon, and chop it into small pieces.

When the potatoes are done, sprinkle the extra bacon on top. Best served warm.