Peel bananas, cut in half. Cut all bananas lengthwise 2 times, and into 1/2-inch pieces, and set aside.
Prepare butterscotch sauce -- in medium saucepan on high, bring butter, sugar, and cream to a boil. Boil on medium for 3 minutes, stirring occasionally. Add banana pieces and stir gently with rubber spatula for 1 minute. Pour into large bowl and place in freezer for 10 minutes to cool a little.
Prepare ice cream -- chop walnuts, set aside. Place cream, marshmallow fluff, and extract into food processor. (Dip rubber spatula into cream for easy removal of marshmallow.) Depending on cream, process for 10-20 seconds or until almost thick or soft peaks. Add walnuts; press down and swirl round with spatula to combine.
Pour this marshmallow cream mixture into 9 X 13 inch pan. Remove sauce bowl from freezer and spoon mixture on top. Gently fold into portions of the cream (do not combine everything together, leave like ripples). Cover with foil and place in freezer until consistency of ice cream, about 4 to 6 hours.
To serve, place a large scoop or two of ice cream in a colorful bowl, sherbet glass, fancy martini glass, or your choice. Garnish each scoop with optional 2 banana chips in the center. And, of course, there's always that bold and beautiful old fashioned ice cream cone.