For The Cake For The Vanilla Buttercream Filling For The Chocolate Ganache

For The Cake

1. Prepare the oven by turning it on and setting the temperature to 180°C [350°F], or 160°C if you're using a fan or convection oven. Prepare a 10 x 14-inch tin by lining it with baking paper, leaving some excess hanging over the edges to make removing the cake easier.
2. Combine the flour, cocoa powder, baking soda, and xanthan gum in a mixing bowl.
3. Add in the caster sugar and give it a stir.
4. Combine melted margarine, soy milk, and vanilla. Mix the wet and dry ingredients, ensuring everything is evenly combined.
5. Transfer the batter into the prepared tin, spreading it evenly to the edges. It will be thicker than your average cake batter, so be sure to get an even distribution.
6. Remove any large air bubbles by tapping the tin on the counter a few times. Bake for 12 minutes.
7. Coat a clean tea towel with unsweetened cocoa powder. You'll need a decent amount, but don't use too much or the cake will become bitter. Do not substitute baking paper for a tea towel, as it won't work.
8. Let the cake cool at room temperature for 5 minutes, then carefully flip it over onto the tea towel.
9. Dust the cake with cocoa powder and slice off any rough or uneven edges using a knife.
10. Gently roll up the cake with the help of the tea towel, placing the cloth in between the cake layers. Refer to the attached post for visuals if needed.
11. Allow the rolled-up cake to cool for 90 minutes at room temperature.

For The Vanilla Buttercream

1. In a large bowl, cream the margarine until it has softened. Gradually add icing sugar, mixing until the batter is smooth. If needed, use soy milk to thin out the batter.
2. Incorporate the vanilla extract and mix thoroughly.
3. Use an electric mixer to beat for about a minute until the buttercream turns light and fluffy.

Finishing The Cake

1. Once 90 minutes have passed, carefully unroll the cake. There is a chance some cracks will appear, but don't worry—you can conceal them if they're small.
2. Spread an even layer of buttercream on the unrolled cake, then gently roll it up again, this time without the help of a cloth.
3. Use a pastry brush to remove any excess cocoa powder, then slice off the edges on both sides to give it a polished look.
4. Cover the cake in plastic wrap and refrigerate for an hour, which will help it hold its shape.

For The Ganache

1. Chop the dairy-free chocolate very finely and add it to a glass bowl along with the soy milk.
2. Place the glass bowl over a small saucepan filled with water, ensuring it doesn't touch the water.
3. Simmer the water in the saucepan over low heat and stir until the chocolate melts completely with no lumps.
4. Remove the bowl from the saucepan using an oven glove or cloth and let it sit at room temperature for exactly one hour.
5. When the hour is up, use an electric whisk to whisk the mixture for about 10 seconds until it becomes light and fluffy. Avoid over-mixing, as the ganache will set too firm to pipe.
6. Transfer the ganache to a piping bag fitted with a large star nozzle. Pipe vertical lines of ganache over the yule log until it's fully covered.
7. If desired, finish with a light dusting of icing sugar.