Prepare a 9x13-inch sheet pan by lightly greasing it and lining it with parchment paper, allowing a bit of the paper to hang over the edges for easy lifting later. Set it aside for now.

Melt the butter in a large pot over medium-low heat. Let it fully liquefy and gently sizzle, allowing it to develop a golden hue and a nutty aroma. The milk solids will sink to the bottom, and a frothy layer will form on the surface. Watch carefully as the solids begin to turn a pale brown. Lower the heat immediately, or, if the butter browns too fast, remove the pot from heat momentarily to prevent overbrowning.

Reduce the heat to low and stir in 7½ cups (397 g) of the marshmallows. Stir constantly and patiently until they melt almost entirely. Avoid the temptation to raise the heat for quicker results, as it can compromise the mixture’s smooth texture.

Once the marshmallows are nearly melted, blend in the vanilla extract and salt. Continue stirring until everything is well incorporated and the mixture becomes silky and smooth.

Add the rice cereal to the pot and fold it gently into the marshmallow mixture. Work swiftly to coat the cereal evenly while keeping the heat low.

Stir in the remaining 1 cup (53 g) of marshmallows. Mix lightly until the extra marshmallows are partially melted and distributed throughout. Avoid excessive mixing to retain pockets of marshmallow for a delightful texture.

Transfer the marshmallow-coated cereal mixture to the prepared pan. Spread it out evenly, using a piece of parchment paper or cling film to press it down gently. Be careful not to pack it too tightly, as this will result in overly dense treats that are hard to bite.

Allow the mixture to cool completely, which will take about an hour. Once set, use the parchment paper overhang to lift the treat block out of the pan. Slice into even pieces with a sharp knife, serve, and enjoy your homemade Rice Krispie treats!