Preheat the oven to 350 degrees(F).
In a large mixing bowl or the bowl of a stand mixer, whisk together the flour, sugar, baking powder, baking soda, cornstarch and salt.
Add the vegan butter, vanilla and 1/2 cup of milk. Begin to beat together with the paddle attachment for the stand mixer or with a hand mixer. Beat until just combined, it will be very thick. Set aside.
In a separate medium sized mixing bowl, whisk together the remaining 1/2 cup of milk, the yogurt and the applesauce.
Now with the stand mixer running or the hand mixer running, slowly pour the wet ingredients into the bowl with the thick batter. Mix until everything is fully combined.
Evenly divide the batter into 2 13x9 inch sheet pans(they are usually called 1/4 size sheet pans), that have been lined with parchment paper. Smooth the batter out evenly in the sheet pans.
Bake for 20-25 minutes or until golden brown and a toothpick comes out clean from the center.
Let them cool completely.
Once the cakes have cooled, make the cream filling. In a medium sized sauce pan, whisk together the non-dairy milk and flour until completely combined and there are no lumps of flour.
Heat on medium, bring to a simmer, whisking constantly, reduce heat to low and let it simmer until very thick. This will only take 1-3 minutes. Turn off the heat and let cool.
Now, in a large mixing bowl or the bowl of a stand mixer, combine the vegetable shortening and vegan butter.
Whip together using the whisk attachment for the hand mixer or stand mixer, until smooth.
Add the sugar, vanilla and salt. Continue to whip until fully combined and fluffy.
Add the cooled thickened milk/flour mixture to the bowl and then continue to whip until the mixture is light and fluffy. This may take a few minutes.
Scoop the cream filling out of the bowl and on to the top of one of the cooled sheet cakes. Smooth it out evenly over the entire cake.
Remove the other sheet cake from the pan and place it on top of the sheet cake that has the cream filling on top. So the cream filling is in the center of the cakes.
Press the top cake down slightly, then chill for at least 4 hours, but I just like to do it a day ahead and chill overnight.
Once the cake has chilled, using a Christmas tree cookie cutter, cut trees out of the cream filled sheet cake. If you use a large one, you should get about 12 trees, but you can use a smaller one and get 18-20.
Now, melt the white chocolate and coconut oil in the microwave in 30 second intervals, stirring after each 30 seconds, until the white chocolate has melted, whisk until smooth.
Dip each Christmas tree into the white chocolate and coat completely. Place them on some parchment paper.
Decorate with red icing and green sugar. Let set until the topping is firm and then enjoy! I use the excess cake and filling to make cake pops! You can roll it all together to make balls, press a stick into the bottom and then coat in the white chocolate!