Preheat the oven to 170°C and grease and line two 20cm sandwich tins with grease proof paper.
Weigh the eggs (in their shells) then weigh the same amount of butter, sugar and flour.
In a large bowl, cream the butter and sugar until pale and fluffy then beat in the eggs, one at a time.
Sift the flour and salt into a clean bowl and carefully add the batter and fold in. Add the vanilla extract and milk and fold in.
Divide the batter between the two cake tins and smooth the tops with the back of a spoon.
Bake for 30 minutes at 170°C, until a skewer inserted into the centre of the cake comes out clean. Transfer to a wire rack to cool.For the Butter Icing:
Cube the butter and whip in a stand mixer or food processor for about 7 mins until pale and doubles in size almost.
Add the icing sugar gradually, sieving it into the mixer/processor. Add the vanilla extract and drops of food colouring and mix well.
Finish with 1-2 tablespoons boiling water to give the icing a lovely glossy finish.
Put a base layer of icing on the cake, making sure it is entirely covered (known as the “crumb layer”). Firm up in the fridge for 20-30 mins until nice and firm.
Take a piping bag fitted with a star nozzle and fill with the rest of the icing. Pipe circular roses onto the base layer of icing until the whole cake is covered. Firm in the fridge for another 20-30 minutes then the cake is ready to serve.