In a saucepan, combine banana, chocolate, brown and granulated sugars, milk,
salt and corn syrup. Stirring constantly, cook mixture over medium heat until
the sugars dissolve. If sugar crystals form on the sides of the pan, wipe them
off with a pastry brush dipped in water.
Clip a candy thermometer to the side of the saucepan, and cook over medium
heat, stirring the mixture occasionally to prevent sticking, until it reaches
the soft-ball stage (236 degrees F).
Remove the pan from the heat.
Add the butter without stirring; cool the mixture until lukewarm (110 degrees
Add vanilla extract; beat fudge until it loses its gloss and starts to thicken.
Pour it into a buttered loaf pan. Sprinkle the fudge with chopped walnuts,
Gently press walnuts into the fudge with a spoon.
When fudge is cool and firm, cut the fudge into 32 pieces.