Line two muffin tins with about 18 muffin/cupcake wrappers, and set aside.
Combine the peanut butter, maple syrup, salt, and agar flakes in a large saucepan over low heat and stir constantly until smooth, hot, melted, and bubbling just a bit.
Add the cereal and ¾ cup of the nuts (if using), and stir until well coated.
Spoon two or three heaping Tbsp of the mix into each muffin wrapper and press into place with the back of a spoon.
Alternately, if you want Krispy squares, you can transfer to mix to an 8 x 8-inch baking dish. Sprinkle with the remaining nuts and refrigerate until completely cool