In a large mixing bowl, beat together the Trex and sugar until light and fluffy, using a wooden spoon or a hand-held electric mixer. Gradually beat in the eggs. Stir in the vanilla extract and milk.
Sift the flour and salt into the mixing bowl and fold in gently using a large metal spoon. Share the mixture between the paper cases. Bake for 20-22 minutes, until risen and golden. Cool in the tin for a few minutes, then transfer to a wire rack to cool completely.
For the icing, beat the butter and icing sugar together until smooth and creamy. Beat in the low fat soft cheese. Split the topping into 2 batches, mixing 2-3 drops of food colouring into each batch. Pipe or spread on top the cakes, then finish off with edible glitter and decorations.