DirectionsStir sugar and 3/4 cup water in heavy large saucepan over low heat until sugar dissolves.
Increase heat and boil without stirring until syrup is deep amber color, brushing down sides of pan with wet pastry brush and swirling pan occasionally, about 14 minutes.
Remove from heat; add cream (mixture will bubble vigorously).
Return pan to medium-low heat; stir until any hard caramel bits dissolve.
Mix in 1/2 cup nuts.
(Sauce can be made 2 days ahead.
Cover; keep chilled.
Rewarm before serving.
Place 2 scoops of ice cream in each of 6 bowls.
Top with banana slices and warm caramel sauce.
Sprinkle each sundae with additional nuts and serve.