Preheat the oven to 180°C / 160°C fan / gas mark 4 and grease and line two 20 cm sandwich tins.
In a large bowl, mix together the self-raising flour, caster sugar, baking powder, and salt.
In a jug, whisk together the dairy-free milk, vegetable oil, vanilla extract, and lemon juice.
Pour the wet ingredients into the dry ingredients and mix until smooth and fully combined.
Divide the mixture evenly between the two tins and smooth the tops.
Bake for 22–25 minutes until risen, lightly golden, and a skewer inserted into the centre comes out clean.
Leave the sponges to cool in the tins for 10 minutes, then transfer to a wire rack to cool completely.
Spread the jam over one sponge, place the second sponge on top, and dust lightly with icing sugar before serving.