Moist lemon drizzle sheet cake without eggs, dairy or gluten.
Preheat your oven to 180°C/350°F (or 160°C/325°F if you're using a fan or convection oven). Line an 8x10-inch tin with baking paper.
Mix the soy milk and lemon juice together and set aside. This will act as your vegan buttermilk.
In a large bowl, cream the margarine and sugar together.
Add the flour, xanthan gum and the bicarbonate of soda. Then add the buttermilk from earlier, mixing it in a little bit at a time. Once you have a smooth cake batter, stir in the lemon zest.
Transfer the batter into your lined cake tin and spread it out evenly. Bake for 30-35 minutes, or until a toothpick through the centre comes out clean.
While the cake is baking, mix together the lemon juice and sugar for the drizzle. Pour and quickly spread it over the cake as soon as it comes out of the oven.
Let the cake cool in the tin for around 20 minutes or until the drizzle on top has dried. Very carefully flip it out onto a wire rack, remove the baking paper and leave it to cool completely.
Mix together the icing sugar and lemon juice and spread a thin layer of the icing onto the cooled cake. Top with extra lemon zest.
Let the cake sit at room temperature until the icing has set, then cut into square slices and enjoy.