Preheat the oven to 150C/300F.
Grease and line a 23cm square cake tin with baking parchment.
Melt the butter, treacle and sugar in a saucepan over gentle heat and leave to cool.
Stir the vinegar into the soya milk and leave to stand for 5 minutes until curdled.
Sift the flour, bicarbonate of soda, salt and spices into a large bowl.
Add the cooled treacle mixture and the milk mixture to the dry ingredients and stir well to combine.
Pour the mixture into your prepared tin and bake in the preheated oven for about an hour. The cake is cooked when a skewer inserted into the centre comes out clean.
Leave to cool in the tin, turn out, cut into squares and store in an airtight container.
