For the blackberry jam: Cook the blackberries in a large, tall stockpot over medium-high heat, stirring to keep the mixture from sticking or scorching, until the berries have broken down and become liquid, 8 to 10 minutes. Add the sugar, and cook, stirring so it doesn't burn, until the mixture is loose and runny. Optionally, if you want to remove the seeds, strain the mixture through a strainer and then return it to the pot before proceeding.
Stir in the pectin a little at a time, following the instructions on the pectin container, until the jam reaches your desired consistency (remember that the jam will continue to firm as it cools). Let cool completely. Refrigerate the jam in an airtight container for up to 1 month.
For the burger: Heat a cast-iron skillet over medium-high heat. When hot, put the patty in the skillet and press it into a flat round burger with a spatula. Sprinkle the burger with salt and pepper and weigh it down with a small plate or empty saucepan; the perfect burger is cooked by placing a weight of some kind on top and only flipping it once during the process. When the burger is halfway done, after 3 to 5 minutes, flip it over, sprinkle with more salt and pepper and cook until desired doneness, another 3 to 5 minutes.
Spread the peanut butter on the bottom bun and 2 tablespoons of the blackberry jam on the top bun. Add the finished burger on top of the peanut butter and flip the top bun over allowing the peanut butter to melt and the jam to ooze all over. Oh and don't forget the napkins.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.