A vegan sandwich cake, filled with dairy-free buttercream and strawberry jam.
Preheat your oven to 180°C (160°C if you're using a fan oven). Line and grease two 7-inch cake tins.
Mix the soy milk and vinegar together and set aside to thicken. This will act as vegan buttermilk.
In a large bowl, mix together the flour and caster sugar.
Add the melted margarine to the bowl, along with the vanilla extract and your vegan buttermilk. Mix well using a wooden spoon, making sure there is no dry mixture stuck to the bottom of the bowl.
Divide the cake batter between the two tins and bake for 25-30 minutes. A toothpick through the centre will come out clean when they're ready. Baking time will vary if you use larger/smaller tins.
Leave the cakes in the tins for 10 minutes then gently flip them out onto a cooling rack and let them cool completely.
Add the margarine to a bowl and gently mix, to soften it a little. Add the icing sugar, a little bit at a time then stir in the vanilla extract. You can add a splash of soy milk if the buttercream is too thick or add more icing sugar if it's too soft.
Place the first cake layer upside-down on a plate or cake stand (or level it out with a knife). Mix the strawberry jam to loosen it, then spread it over the cake.
Pipe or spoon your buttercream on top of the jam and use a palette knife to smooth it out, leaving a small gap around the edges to prevent it from spilling out. Gently place the second cake layer on top, right side up.
Sift a small amount of icing sugar over the top of the cake, cut into slices and enjoy!