Preheat the oven to 350°F and grease a bundt pan.
Start by making your vegan buttermilk, which is done by combining non-dairy milk with either apple cider vinegar, white vinegar, or lemon juice. Mix together and let it stand for 5-10 minutes to curdle while prepping the other ingredients.
Mix together the gluten free flour, cornstarch, baking powder, and salt in a small bowl and set aside.
Zest oranges for the cake batter. I think 2 is perfect, but you can use a little more or less. In a large bowl, mix the orange zest with the granulated sugar until it has the consistency of soft crumbs. Then add in the softened vegan butter and cream together until it is soft and fluffy.
Next, add the vegan buttermilk, champagne, unsweetened applesauce, and vanilla extract into the large bowl and mix with the sugar/vegan butter mixture. This will look separated, as the butter will appear chunky and not smoothly combined with the other wet ingredients. This is okay and correct.
Finally, add the dry ingredients in and mix until combined. This now will appear smooth, but make sure not to overmix as that can cause the cake to be tough.
Pour the batter into a well-greased bundt pan and put in the oven for 37-42 minutes, testing for doneness by inserting a toothpick or a knife and making sure it comes out with crumbs, no wet batter. When it’s done, take out of the oven and put the pan onto a cooling rack. Let it sit for about 10 minutes before inverting the cake onto the cooling rack to remove it from the pan.
Lastly, make the icing by mixing the powdered sugar, orange juice (or non-dairy milk if you don’t want the icing to be orange flavored), and orange zest in a small bowl. I find 3-4 teaspoons of liquid to be perfect, but you can use more or less depending on the consistency you want. Pour the icing over the top of the cake.
Eat and enjoy!