Fill a small pot with 1/2 cup of water and bring it to a boil over medium-high heat. Place a large heatproof bowl on top of the pot, ensuring that the bowl doesn't touch the simmering water. This setup will gently melt your ingredients without burning them.

Add the unsalted butter and plain marshmallows to the heatproof bowl. Continually whisk the mixture over the simmering water until it forms a smooth paste, which should take about 2-4 minutes. Be patient and keep stirring to avoid any lumps or burning. I like to use a silicone spatula for scraping the sides of the bowl to make sure everything is evenly melted.

Remove the bowl with the melted marshmallow mixture from the heat, using oven mitts or a tea towel to protect your hands. Whisk in the salt and add a drop or more of red food coloring to achieve your desired shade. Mix until the color is evenly distributed.

Place the puffed rice cereal in a large mixing bowl. Pour the warm, colored marshmallow mixture from Step 3 over the cereal. Use a spatula or wooden spoon to mix thoroughly, making sure all the cereal is well coated with the marshmallow mixture.

Oil your hands lightly to prevent sticking, then scoop handfuls of the mixture and shape them into oval 'brain' shapes. Use a butter knife to create a dent in the center of each brain. Dip a toothpick in red food coloring and draw veins on the tops for a realistic effect. Store in an airtight container for up to a week. For extra fun, I sometimes sprinkle a little red sugar on top for more 'gory' detail!