Start by making the vegan buttermilk. Warm the oat milk, whisk in the apple cider vinegar and set to one side.
Grease and line 3 x 20cm sandwich tins. Pre heat the oven to 200C/ 180C fan.
In a mixing bowl, sieve the plain flour, caster sugar, cocoa powder, baking powder and bicarbonate of soda.
Add the melted vegan butter, vanilla extract and red gel food colouring to the buttermilk. Whisk well.
Add the wet ingredients to the dry. Fold the mixture gently until the mixture is just combined.
Evenly distribute the mixture between the 3 baking tins. Place in the oven for 22-25 minutes. The cake is ready when it is well risen and pulling away from the sides of the tin. A toothpick inserted in the middle should come away with loose, moist crumbs.
Leave the sponges to cool in their tins for 10 minutes, then carefully turn out onto wire racks and leave to cool completely.
Meanwhile prepare the cream cheese frosting. Using a stand mixer or electric whisk, cream the vegan butter and vegan cream cheese. Add the sifted icing sugar in thirds, mixing for a minute in between each addition. Once well mixed and smooth, add the cornflour and mix for a further minute. Place in the fridge until you're ready to ice the cake.
To assemble the cake, level off the 3 sponges with a serrated knife, if necessary. Place one sponge on a cake stand. Add approximately 3tbsp of cream cheese frosting. Spread over the sponge. Layer over the second sponge and repeat the spreading of the cream. Layer over the third sponge. Apply a thin layer of icing over the top and sides of the cake. Pipe over the remaining buttercream and decorate with freeze dried strawberries and red velvet dusting.
Place in the fridge until ready to serve.