Preheat oven’s broiler on high, about 5 minutes.

Line a baking sheet with aluminum foil. Spray the foil with nonstick cooking spray. Spread half of the mini marshmallows (one 10-ounce bag) in a single layer on the prepared baking sheet. Broil on the center rack until the marshmallows are toasted and golden-brown on top, which only takes a couple of minutes. Keep a close eye on them so they don’t burn. Remove from oven and set aside.

Line a 9×13-inch baking pan with parchment paper. Lightly grease the parchment. I always use a very light mist of nonstick spray. Set aside.

Melt the butter in a very large pot over medium heat. Once melted, add the remaining 10 ounces of (non-toasted) marshmallows. Stir the mixture with a rubber spatula until the marshmallows are completely melted.

Remove from heat, then immediately stir in the vanilla extract and salt. Fold in the crispy rice cereal and graham cracker pieces until mostly combined. Allow to slightly cool for a minute or two, and then fold in the chocolate and toasted marshmallows.

Transfer mixture to prepared pan. Using a rubber spatula (greasing it lightly helps), gently spread mixture to fit the pan. Lightly grease the back of a flat spatula and very gently press the mixture down into the pan. Do not pack it down with force, just lightly press down until it is secure in the pan.

Allow treats to set for at least 1 hour at room temperature, and up to 1 day. Cover tightly if leaving out for more than a few hours.

Drizzle melted chocolate over the top of the cooled treats, if using, and place in the refrigerator for about 15–20 minutes to set the chocolate. (Not too much longer, or the treats will be too hard to cut.)

Lift the rice krispie treats as a whole out of the pan using the edges of the parchment paper. Cut into squares.

Cover and store leftover treats at room temperature for up to 3 days. To store, place in an airtight container, with sheets of parchment or wax paper between layers.