Preheat the oven to 400°F. Line a cookie sheet with aluminum foil. Place raw bacon on top of foil and bake for 12-15 minutes until desired crispness. Set aside.
Slice up the jalapeño how you like it. Set aside.
Slice the sourdough bread into moderately thick slices. Spread a good amount (2 Tbsp+) of blackberry jam on each slice.
Build each sandwich with bacon, cheese and jalapeño on the blackberry-laden sourdough bread.
Preheat a skillet or electric griddle to medium/high heat (about 325°F). Place sandwiches buttered side down and toast until a medium golden brown. While cooking, add a good amount of butter to the top side of the bread.
Flip and cook the other side until a beautifully crisp and light brown. If the bread is toasting too quickly before the cheese melts, lower the temperature and allow the cheese to fully melt.
Slice on the diagonal for that optimal first bite. And enjoy!