1Preheat the oven to 170C/150C Fan/Gas 3. Grease and line 4 x 18cm sandwich tins.
2Put the eggs, Stork spread, sugar and flour in a bowl and beat until smooth using a hand-held mixer (or a stand mixer, if you have one).
3Divide the batter evenly between 4 bowls, then colour each batter with the pink food gel to get 4 different shades of pink by stirring 2 drops into the first bowl, 4 drops into the second, 6 drops into the third and 8 drops in the fourth. Spoon each different shade of batter into each of the four tins and bake them for 27-30 minutes, until the tops spring back when lightly pressed with a finger.
4Cool in the tins for 5 minutes, then turn out onto wire racks, before removing the baking paper; leave to cool completely.
5If necessary, trim the raised tops of the sponges with a sharp knife to flatten them. Place the darkest pink sponge onto a cake stand first, then spread with 1/3 of the jam. Top with the next darkest sponge and spread with more jam; repeat with the rest of the sponges.
6For the buttercream, beat together the Stork spread, icing sugar and vanilla paste (if using), until the mix is light and fluffy.
7Use about 1/3 of the icing to spread all over the cake to form a crumb coat, then chill the cake for 20 minutes to firm.
8Meanwhile, to make the different shades of icing, divide the remaining buttercream between 4 bowls. Set aside one bowl of white buttercream, then colour the 3 remaining icings with the pink food gel: stir 2 drops into one bowl; 4 drops into the second bowl and 6 drops into the third bowl. Put the 4 icings into 4 separate piping bags with medium star nozzles.
9Take the cake out of the fridge and, starting with the darkest shade of pink buttercream, pipe roses around the base of the cake. Use the second darkest buttercream to pipe another ring of roses, then repeat with the final shade of lighter buttercream. Finally, use the reserved white icing to pipe roses all over the top of the cake.
10Store in the fridge, and an hour before serving, take the cake out to warm to room temperature.