Prepare your workspace; coat a 9x9-inch baking pan with cooking spray and line with parchment paper.

In a large saucepan over medium heat, melt 4 tablespoons of butter, then stir in the marshmallows until completely melted, about 4-5 minutes.

Remove from heat and stir in 1 teaspoon of vanilla extract and 1/3 cup pistachio butter until well combined.

Fold in 6 cups of puffed rice cereal until each piece is coated.

Transfer the mixture into the prepared pan and press firmly into an even layer.

Melt 1/2 cup chocolate chips in the microwave, stirring every 30 seconds until smooth. Stir in 1 teaspoon of coconut oil if using.

Pour the melted chocolate over the pressed rice mixture, drizzling the remaining tablespoon of pistachio butter, and swirl together.

Sprinkle with 1/4 cup of chopped pistachios and a pinch of flaked sea salt on top.

Chill at room temperature for 30 minutes, then refrigerate for at least 1.5 hours before slicing into squares.