Preheat oven to 350 degrees F. Adjust oven rack to lowest position.
Line a 9x13-inch baking pan with foil, leaving about a one-inch overhang on all sides. Spray foil with cooking spray or oil.
Heat water to boiling in a medium pan on the stovetop. Reduce heat and whisk in cocoa until smooth.
Remove from heat and whisk in chopped chocolate until melted and smooth.
Whisk in melted cannabutter and butter.
Whisk in eggs and vanilla and continue to whisk until smooth and well mixed.
Whisk in sugar until fully incorporated.
Stir in flour and salt and mix with a wooden spoon or rubber spatula until just combined.
Pour batter into prepared pan and use a rubber spatula so spread evenly to the edges in a uniform layer.
Bake for about 30 minutes or until a toothpick inserted halfway between edge and center comes out with just a few moist crumbs.
Transfer pan to wire rack to cool completely, about 1 1/2 hours, before proceeding.
Prepare Peanut Butter Filling:
Beat together the peanut butter, butter and salt with an electric mixer until smooth and creamy, about 2 minutes. Reduce the speed to low gradually beat in confectioner’s sugar. Beat in vanilla extract. Increase the speed to medium-high and add milk, a tablespoon at a time, until you get a smooth very thick, yet spreadable, consistency. If it seems a too dry, add another splash of milk, too loose, don’t add as much milk. The consistency of your peanut butter will have a lot to do with it.
Use a rubber or offset spatula to spread the peanut butter filling in an even layer over the cooled brownies in the pan.
Melt together the chocolate chips and peanut butter in the microwave on 50% power, stirring every 30 seconds, until completely smooth and melted. Pour the mixture over the peanut butter layer and spread into an even layer with a rubber or offset spatula.
Refrigerate for at least 30 minutes.
Using foil overhang, carefully lift brownies out of the pan onto a cutting board. Cut into squares and serve.
Store in an airtight container at room temperature for up to 5 days or freeze for longer storage (see notes at top of page).