Melt butter in large skillet, over high heat. Cook until butter browns. Add brown sugar and 1/4 cup sugar; cook about 2 minutes, stirring constantly until bubbly.
Add bananas and cook 3 minutes. remove from heat and stir in rum. Return to low heat and cook 3 minutes, stirring constantly or until most of the liquid has evaportated.
Removefrom heat, spoon into a blender or food processor and process till smooth. Pour into a blowl and refrid till cool.
Preheat oven to 375 degrees. Lightly butter four 8 oz ramekins and sprinkle each with 1/4 tsp sugar. Place egg whites in a large bowl; beat witha mixer at high speed until foamy. Add cream of tartar; beat till soft peaks form. Gradually add remaining 1/4 cups sugar; beat till stiff peaks form.
Pour chilled banana mixture into a large bowl. Add chocolate chips. Fold in egg whites. Spoon into baking dishes; piling mixture above the rims. Bake 15-18 minutes.
Dust with powdered sugar and serve.