Preheat the oven to 350ºF (177ºC). Spray a 6-serving silicone snowflake mini cake mold* with nonstick spray. Use a small pastry brush to brush the spray into all of the crevices. Tap out any excess spray. Place the mold on a baking sheet.
In a large bowl, whisk together the cake flour, baking powder and salt. Add the sugar and whisk to combine. Add the butter and beat, with an electric mixer on low speed, until the butter is evenly distributed and the mixture looks like crumbs with no large chunks.
In a medium bowl, whisk together the milk, egg whites, oil and vanilla. Slowly add the milk mixture to the flour mixture and continue beating on low until smooth, about 1-2 minutes.
Transfer the batter to the prepared pan, evenly distributing the batter and filling the cavities a little more than half full. Bake until the tops of the cakes are light golden and a toothpick inserted into the centers of the cakes comes out clean, about 18-22 minutes. Be careful not to over bake. Let the cakes cool in the pan for about 7 minutes then turn the cakes out onto a cooling rack to cool completely.
Brush one or two coats of vanilla icing on the tops and sides of the cakes. Decorate as desired. I used fine opal sanding sugar, candy snowflakes and candy pearls.
In a medium bowl, whisk together the powdered sugar, butter, vanilla, salt and 1 tablespoon of milk until smooth. Add additional milk as need to achieve your desired consistency.
I used a 6-serving silicone mold with 3-inch diameter, 1-inch deep cavities.