For the cake: Preheat the oven to 350 degrees F. Grease two 9-inch cake pans with baking spray.
Mix together the cake mix, flour, sugar, baking soda and salt in a medium bowl.
In a mixer with the whisk attachment, mix together the egg whites, vegetable oil, sour cream, vanilla, bananas and instant pudding until well mixed. Add the dry ingredients and then then slowly pour in 1 1/3 cups water.
Divide the batter between the prepared cake pans.
Bake until a toothpick inserted into the center of the cakes comes out clean, about 40 minutes. Cool on a rack.
For the praline: In a medium saucepan, bring the sugar and 1/2 cup water to a boil without stirring; occasionally swirl the pan gently to blend the sugar. Once the mixture has turned a light caramel color, remove the pan from the heat and add the vanilla and the candied pecans. Stir with a spatula and immediately pour out onto a parchment-lined cookie sheet. Allow to dry until brittle. Break into pieces.
For the buttercream: Put the sugar and egg whites in a large heatproof bowl set over a saucepan of simmering water. Whisk constantly until hot to the touch; the sugar should be dissolved and look like marshmallow cream.
Pour the mixture into the bowl of a stand mixer fitted with the whisk attachment. Beat on medium speed until the egg whites cool and form a thick, shiny meringue, about 5 minutes. Switch to the paddle attachment and add the butter, 1 tablespoon at a time, beating until smooth. Once all the butter is in, add the vanilla and beat on medium-high speed until thick and very smooth, 6 to 10 minutes. Refrigerate.
To assemble the cake: Mix 1 cup of the crushed praline into 2 cups of the buttercream. Spread the top of one of the cake layers with the praline filling, then stack the second cake layer on top. Ice the entire cake with the remaining buttercream.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.