Preheat the oven to 375 degrees F (190 degrees C).
Bring a large pot of salted water to a boil, then add potatoes and return to a boil. Cook until very tender, 14 to 16 minutes. Drain potatoes and add them to a large bowl.
Meanwhile, cook bacon until crisp in a large skillet, drain, and set aside. Reserve drippings in pan.
Add jalapenos to drippings, and cook, stirring constantly until softened, about 2 minutes. Add jalapenos to potatoes.
Add in reserved bacon, pimento cheese, 1 ½ cups pepper Jack cheese, and salt. Stir to combine (potatoes will fall apart). Transfer mixture to a casserole dish and top with remaining cheese.
Bake in the preheated oven until browned and bubbly, about 20 minutes.
