Add egg white, corn syrup and salt to a large bowl and mix with an electric mixer on high speed 5 minutes.
Add sugar and mix on low speed until combined then add vanilla and mix until combined.
Spread marshmallow fluff on a piece of bread and peanut butter on another.
Sandwich the two pieces together.
Notes
I made this with plain and buttery toasted bread. I liked plain ol' bread the best. The fluff makes a lot and there are many other recipes on the internet you could use the fluff in.
Recipe by The Spice Kit Recipes at https://www.thespicekitrecipes.com/massachusetts-fluffernutter-sandwich/