Preheat the oven to 325 degrees. In a bowl, use a pastry cutter to cut together the butter, flour, brown sugar, oats, and salt until the mixture is slightly crumbly. Sprinkle in a couple of tablespoons of water if it seems too dry.
Split the muffins and spread on a thin layer of peanut butter, followed by jelly. Sprinkle the streusel topping evenly over the 8 muffins and pop it in the oven for 10 minutes. Turn up the heat to 350 and bake for another couple of minutes or until slightly golden on top.