Put butter, sugar and corn syrup in a medium-size saucepan and heat until mixture begins to bubble; boil 1 minute.
Stir in evaporated milk and cook 3 to 4 minutes or until sauce is hot and bubbly.
Add chopped peanuts.
In a small bowl, blend cornstarch with 2 tablespoons water.
Add to sauce and heat until thickened.
Pour sauce into fondue pot and place over burner at the table.
Serve with popcorn, cubes of apple, pear and banana.