Grease a 9x13-inch pan with butter, oil, or cooking spray. Alternatively, you can line it with parchment paper, leaving some overhang on the sides for easy removal.
In a large pot over low heat, melt the butter. Once melted, add the peanut butter, marshmallows, vanilla extract, and salt. Stir continuously until completely melted and smooth, about 3-4 minutes.
Remove the pot from the stove and stir in the crispy cereal until just combined. Move quickly to transfer the rice krispie treats to your prepared pan.
Gently press the cereal mixture into an even layer with a rubber spatula.
Melt chocolate chips and coconut oil in a microwave-safe bowl, in 30-second intervals, stirring in between. Pour the melted chocolate over the bars and use the back of a spoon or an offset spatula to spread the chocolate to the edges of the pan.
Let cool at room temperature or in the fridge for 1-2 hours before cutting into squares.