sprinkles or edible sugar, for decorating (optional)
Preheat your oven to 350F. Lightly grease a 9 x 13 inch baking pan and line the bottom with a piece of parchment.
Sift the flour, baking soda, baking powder, and spices into a large mixing bowl. Add the salt.
In a separate large bowl, mix together the sugar, oil, vanilla, buttermilk, and applesauce. Pour these wet ingredients into the dry ingredients. Use a hand mixer or whisk to mix the batter well, until no visible lumps remain.
Pour the cake into your cake pan and bake for 35 minutes, or until the top is firm and set or a toothpick inserted into the center comes out clean. Check at 30 minutes if your oven is hot, and give it an extra 5 minutes if it's not ready at 35 minutes. When the cake is done, allow it to cool completely (1-2 hours).
When the cake is ready, or in advance, prepare the frosting. Add the butter and cream cheese to the bowl of a stand mixer fitted with the paddle attachment (alternately, use a hand mixer on medium low speed). Beat for a few minutes on medium low speed, then add the vanilla and incorporate it fully. Add the sugar, one cup at a time, beating on low speed. Switch to the whisk attachment if using a stand mixer, then continue to beat on medium speed until the frosting is fluffy and smooth.
Use an inverted spatula to cover the cake with frosting. Garnish with sprinkles, if you like. Cut into 12-15 slices and serve!
In place of the flour, you can use a GF flour blend that you trust.