Spray an 8x8 square pan with cooking spray (or lightly oil it). Line the pan with heavy duty foil (or regular foil that’s been doubled) so that two ends extend over the edges of the pan. (You can also use parchment paper to line the pan.) Spray the foil (or parchment) with cooking spray. Set aside. Also spray a large pot or Dutch oven and a large spoon or spatula with cooking spray.

Heat the butter in the prepared pot over medium heat. After the butter melts it will start to sizzle a bit and a white foam will develop on the top. If it’s splattering too much reduce the heat a bit. Continue cooking for 3-5 minutes until the butter gets silent (stops sizzling) and the foam turns a deeper yellow. Start swirly the pan occasional at this point until the butter turns golden brown and has a nutty aroma.

Turn down the heat to the lowest setting and add 12 ounces (about ¾) of the marshmallows to the butter. Stir (with the oiled spatula or spoon) until the marshmallows melt and the mixture is smooth. Add the vanilla bean seeds or vanilla bean paste (or vanilla extract) and stir to combine.

Add all of the rice cereal and stir until well combined. Then add the remaining 4 ounces of mini marshmallows and stir to distribute and just until they’re beginning to melt (you want little pockets of marshmallow).

Transfer the mixture to the prepared pan. With slightly wet fingers, press the mixture lightly into the pan. Don’t pack it in or the bars will be dense. Sprinkle the top lightly with flaky sea salt, if desired.

Allow to cool and enjoy! You can store the treats in an airtight container at room temperature for 2-3 days. They also freeze well.