In a large saucepan, melt butter and half of the marshmallows (5 ounces) over medium-low heat. Stir until the marshmallows are fully melted.
Once melted, mix in peanut butter, maple syrup, vanilla extract, cinnamon, and salt. Turn off the heat.
Add rice krispies, peanuts, and the remaining marshmallows (5 ounces) to the saucepan. Stir well until all ingredients are evenly coated.
Transfer the mixture to a 9x13" pan lined with parchment paper. Press the mixture into an even layer using the flat bottom of a measuring cup or your hands. Refrigerate while you prepare the ganache.
For the ganache, melt chocolate chips in the microwave or using a double boiler. Whisk in the milk/cream and vanilla extract.
Spread the ganache over the peanut butter rice krispies, top with flaky salt (optional), and refrigerate for at least one hour or until the ganache sets.