Butter a 7-inch cake pan.

Mix the melted butter, sugar, egg, vanilla extract and bananas together in a large bowl. In a second bowl, combine the sour cream and the baking soda. In a third bowl, combine the flour, baking powder and salt. Finally, in a fourth bowl, combine the chocolate chunks, brown sugar and cinnamon. Add the flour mixture to the butter mixture, alternating with the sour cream mixture. Pour half of the batter into the buttered cake pan. Scatter half of the chocolate chip mixture on top. Cover with the remaining batter and then sprinkle the remaining chocolate chip mixture on top. Wrap the pan completely in a piece of well-greased aluminum foil.

Place a rack in the bottom of the pressure cooker and add 2 cups of water. Lower the cake pan into the cooker using a sling made of aluminum foil (fold a piece of aluminum foil into a strip about 2-inches wide by 24-inches long). Fold the ends of the aluminum foil into the cooker and lock the lid in place.

Pressure cook on HIGH for 50 minutes.

Let the pressure drop NATURALLY and carefully remove the lid. Remove the cake pan from the cooker and let it cool. Transfer the cake to a serving plate and serve with a dollop of whipped cream if desired.