Preheat your oven broiler to high. Line a baking sheet with foil and lightly coat it with nonstick cooking spray.

Spread one 10-ounce bag of mini marshmallows onto the prepared baking sheet in a single layer. Place them under the broiler and toast until the tops are golden brown. Keep a close eye on them, as marshmallows can go from toasted to burned very quickly. Remove from the oven and set aside.

Line a 9x13-inch baking dish with parchment paper, leaving some paper hanging over the sides for easy removal. Lightly spray the parchment with nonstick cooking spray.

Melt the butter in a large pot over medium-low heat. Add the remaining 10-ounce bag of mini marshmallows and stir frequently until the marshmallows are completely melted and the mixture is smooth.

Remove the pot from the heat. Stir in the vanilla bean paste and salt until combined.

Add the Rice Krispies cereal and graham cracker pieces to the marshmallow mixture. Gently fold everything together until the cereal and graham crackers are evenly coated.

Allow the mixture to cool slightly, then gently fold in the milk chocolate pieces and toasted marshmallows. Mix just enough to distribute them throughout while leaving plenty of gooey marshmallow and chocolate pieces intact.

Transfer the mixture to the prepared baking dish. Using a lightly greased spatula or a piece of parchment paper, gently spread it into an even layer. Don’t press the mixture down too firmly, which can make the treats hard instead of soft and chewy.

Let the treats cool and set at room temperature for about 1 hour.

If using the optional chocolate topping, melt the 2 milk chocolate bars and drizzle the chocolate over the cooled treats. Allow the chocolate to set before slicing.

Lift the treats from the pan using the parchment paper, then cut into squares and serve.