Brownie Sundaes with Banana Chips

For sauce: Bring cream to simmer in medium saucepan.
Remove from heat.
Add chocolate; stir until smooth.
(Sauce can be prepared 1 day ahead.
Cover; chill.
Rewarm sauce over low heat before serving.)
For brownies: Preheat oven to 350F.
Butter 13x9-inch metal baking pan.
Line bottom with parchment paper.
Butter paper; dust sides of pan and paper with flour.
Tap out excess.
Melt both chocolates and butter in heavy large saucepan over low heat, stirring until smooth.
Cool to room temperature.
Using electric mixer, beat 1/2 cup sugar and yolks in large bowl until thick, about 4 minutes.
Stir in chocolate mixture.
Using electric mixer fitted with clean dry beaters, beat egg whites in another large bowl until soft peaks form.
Gradually beat in cup sugar.
Continue beating until stiff peaks form.
Using rubber spatula, gently fold whites into chocolate mixture in 3 additions.
Pour batter into prepared pan.
Bake until brownie cracks around edges and tester inserted into center comes out with moist crumbs attached, about 35 minutes.
Cool on rack.
(Can be made 1 day ahead.
Wrap tightly; store at room temperature.)
Run knife around sides of brownie.
Place baking sheet atop pan; invert brownie onto baking sheet.
Remove pan.
Peel off parchment.
Invert brownie onto another baking sheet.
Cut into 12 pieces.
Place 1 brownie in center of each plate.
Sprinkle with powdered sugar.
Top with ice cream.
Spoon sauce over.
Sprinkle with banana chips and serve immediately.