Preheat the oven to 350 degrees F.
Cut the jalapeño lengthwise creating a pocket for the filling. Leave the stem intact. Carefully scrape the inside of the jalapeño with a paring knife to remove the seeds.
In a small bowl, combine the cream cheese, cheddar cheese, and the bacon. Place the mixture in a resealable storage bag and cut one corner of the bag that will allow the mixture to be easily piped into the peppers. Squeeze the mixture to the bottom of the bag and fill each pepper with the cream cheese mixture. Press the edges of the pepper back together.
In a medium bowl, combine the flour, cayenne, garlic powder, eggs, and buttermilk and mix until the mixture looks like the consistency of pancake batter. It needs to be thick, but if you find that it is too thick, add a little more buttermilk. Place the Panko crumbs on a third dish. One at a time, coat the jalapeño in the batter, then press the jalapeño into the Panko crumbs gently to assure that the Panko adheres the jalapeño.
Place each pepper cut side up on a cookie sheet and spoon butter on top of each pepper. Bake for about 30 minutes or until the top is golden. Remove from the oven and transfer jalapeños to a serving dish and sprinkle with a little extra salt.reheat the oven to 350 degrees F.