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, about 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 the pan.

Add jalapenos to reserved bacon drippings and cook, stirring constantly until softened, about 2 minutes. Add jalapenos to potatoes.

Add in reserved bacon, pimento cheese, 1 1/2 cups pepper Jack cheese, and salt. Stir to combine (potatoes will fall apart). Transfer mixture to a casserole dish and top with the remaining cheese.