Preheat the oven to 180°C/Gas Mark 4. Lightly grease both the top and bottom ring and dust with flour.
Sift the flour, salt, bicarbonate of soda and baking powder into a bowl. In a separate large mixing bowl, beat the butter and sugar until pale and fluffy, then add the lemon zest. Add the eggs, a little at a time, beating well between each addition. Mix the buttermilk and lemon juice in a jug. Fold the flour mixture into the butter mixture, alternating with the buttermilk and lemon juice mixture.
Divide the cake mixture between the two parts of a Fillables Fluted Ring Cake Tin, level the tops, then bake for 35-45 minutes, or until a skewer inserted into the cakes comes out clean – there will be a difference between baking times as the top tin is shallower than the bottom. Leave the cakes to cool in the tins for 10 minutes before turning out onto a wire rack to cool completely.
To assemble the cake, place the bottom layer onto a serving plate. Spoon a little of the frosting into each cavity, then divide the pearls evenly between the cavities. Spread the remaining frosting over the bottom layer of the cake, then top with the top layer.
To decorate, mix the icing sugar with the pink food colouring and enough water to make a smooth icing. Drizzle the icing over the cake, letting it run down the sides, then top with the lemon zest.