Preheat your oven to 325°F (160°C) and line a ¼ sheet pan with parchment paper, greasing the sides with butter.

In a large mixing bowl, sift together the all-purpose flour, Instant Clearjel, baking powder, baking soda, and salt, whisking until evenly combined.

In a separate bowl, mix the buttermilk, water, vanilla extract, almond extract, and apple cider vinegar, stirring gently until well mixed.

Beat the softened salted butter and granulated sugar together until light and fluffy, then drizzle in the vegetable oil and light corn syrup, mixing well.

Incorporate the whole egg into the butter-sugar mixture and alternate adding the dry mixture and wet ingredients, mixing on low speed just until combined.

Whip the egg whites with cream of tartar until stiff peaks form, then carefully fold the whipped egg whites into the cake batter.

Spread the batter evenly into the prepared ¼ sheet pan and bake for approximately 24-26 minutes, until a toothpick comes out clean.

Remove the cake from the oven, let it cool in the pan for 10 minutes, then invert onto a wire rack to cool completely and wrap in plastic wrap to freeze.

Prepare the creamy vanilla buttercream by beating cream cheese, softened butter, and shortening until smooth, then add powdered sugar and extracts.

Layer on the creamy vanilla buttercream generously once the cake is cooled, and decorate if desired.