Heat oven to 350°F Combine sugar and 1 cup butter in large bowl. Beat at medium speed, scraping bowl often, until creamy. Add eggs; continue beating until well mixed. Reduce speed to low; add bananas and 1/4 teaspoon rum extract. Beat until well mixed. Add all remaining cake ingredients. Continue beating, scraping bowl often, just until mixed.
Pour into greased 13x9-inch baking pan. Bake for 35 to 40 minutes or until toothpick inserted in center comes out clean. Cool, uncovered, at least one hour.
Meanwhile, combine brown sugar, water and corn syrup in small saucepan. Cook over medium heat, stirring constantly, until sugar is completely dissolved (3 to 4 minutes). Add 5 tablespoons butter; continue cooking until butter is melted (1 to 2 minutes). Remove from heat; stir in condensed milk and 1/4 teaspoon rum extract. Cool 15 minutes.
Beat whipping cream in small bowl at high speed until soft peaks form. Continue beating, gradually adding powdered sugar, until stiff peaks form.
To serve, place individual cake servings onto dessert plates. Drizzle with about 1 tablespoon sauce. Dollop with whipped cream; sprinkle with cashews, if desired. Drizzle with additional sauce. Store refrigerated.