Line two cookie sheets with parchment. Set aside.
In a large saucepan, add the sugar, corn syrup, and vanilla. Bring to a low boil, stirring frequently.
Carefully add the peanut butter and pinch of salt and stir until the peanut butter is fully incorporated. Turn heat off.
Add in the Chex cereal and stir well, making sure each piece is coated.
Pour marshmallows in and stir until evenly dispersed, but not too long. The marshmallow will start to melt, but you do not want them to melt completely.
Using a 2-tablespoon scoop, scoop out mounds of the chex mixture onto the cookie sheet. They will not spread much, so you can place them close together.
Let sit for about 30 minutes so they can firm up.
Store in layers in an airtight container.