Preheat the oven to 325 degrees F (165 degrees C). Spray two 11x17-inch baking sheets with cooking spray and line with parchment paper. Spray the parchment paper with cooking spray.

Mix cake mix, flour, sugar, and salt in a medium bowl.

Place water, sour cream, oil, vanilla, almond, and egg whites in the bowl of a stand mixer fitted with the paddle attachment. Mix on low speed until combined; slowly add the flour mixture. Beat together on medium speed for 2 minutes.

Pour 1/2 of the batter into each baking sheet, and spread into an even, thin layer.

Bake in the preheated oven until the edges are light golden brown and the center is set, 12 to 15 minutes. Cool completely on a wire rack for at least 30 minutes.

Transfer one of the cooled cake layers, along with the parchment, onto a cutting board. Spread raspberry preserves over 1/2 of the cake, and blueberry preserves over the other. Spread a layer of cream cheese frosting over the second cake layer; flip frosted side over the preserves. Spread remaining frosting over the top. Slide the cake on its parchment onto a cookie sheet, cover with plastic wrap, and freeze for 1 hour or chill overnight.

Cut the chilled cake into 2-inch squares by first marking with a ruler. Place squares on a wire rack over a parchment lined baking sheet. Return to the fridge to chill.

Whisk powdered sugar, water, corn syrup, almond, and vanilla together in a glass bowl.

Fill a small sauce pot with an inch or two of water; bring to a simmer. Place sugar mixture on top of the simmering water. Whisk until icing is smooth and temperature reaches 92 degrees F (33 degrees C). Add white chocolate chips and any food coloring and stir until melted. Turn off heat but leave double boiler on the stovetop to keep icing pourable.

Ladle the warm icing over the top of each cake square. Quickly add sprinkles; icing should set quickly since the cake is cold. Let petits fours set in the refrigerator for about 5 minutes, or at room temperature for 30 minutes.