Preheat the oven to 180°C/gas mark 4. Grease and line a non-stick 20cm square cake tin with baking parchment.
In a large mixing bowl, use an electric hand whisk to cream together the butter, sugar and vanilla extract until light and fluffy. Beat in the eggs one at a time, adding a little flour with each egg to stop the mixture splitting. Sift over the remaining flour, baking powder and red food colouring, then gently fold together using a wooden spoon until the mixture is smooth and evenly coloured. Spoon the mixture into the tin and bake for 30 minutes, or until a skewer comes out clean. Turn the cake out on to a wire rack and allow to cool.
Once cooled, place the pink square sponge cake on a surface and cut out 9 hearts with a 5cm heart cutter. Brush the hearts on one side with the apricot glaze and stick together to make a long heart-shaped cake. Measure the length of your loaf tin and cut the heart-shaped cake to size. Transfer to the freezer and chill for 30 minutes.
Meanwhile, make the second Victoria sponge cake mixture. Use the same method as in step 2, but without the food colouring. Once made, spoon 2-3 tbsp of the Victoria sponge mixture into the bottom of the loaf tin and spread it out in an even layer. Place the heart cake on top, pointed end upwards. Gently spoon the remaining sponge mixture around and over the heart cake, covering it fully. Don’t worry if the heart looks as though it is sticking out slightly – the plain Victoria sponge mixture will rise during baking to come up the sides and cover it completely.
Bake for 45-50 minutes until cooked through, or until a skewer comes out clean. Allow to cool with the loaf tin set upside down on a wire rack so the cake begins to come away from the sides of the tin. You may need to run a knife around the edge of the cake to help it slide out.
Meanwhile, make the biscuit dough. Turn the oven up to 190°C/gas mark 5. In a large mixing bowl, use an electric whisk to cream the butter with the sugar until well mixed and just creamy in texture. Do not overwork, or the biscuit will spread during baking.
Beat the egg again until well combined, and add 1 tbsp to the creamed butter and sugar. Discard the remaining egg. Add the flour and beat on low until a dough forms. Gather into a ball, wrap in clingfilm and chill for at least 1 hour. Roll out the biscuit dough to 4mm thick and cut out a 12cm heart using the cookie cutter. Place on a non-stick baking tray and bake in the preheated oven for 12 minutes until beginning to turn golden around the edges. Set aside to cool on a wire rack.
Next, make the white chocolate buttercream. In a large mixing bowl, use an electric hand whisk to beat together the butter and vanilla extract for 2-3 minutes, until pale and soft. Add half the icing sugar and beat on a low setting at first, so the icing sugar doesn’t puff up and out of your bowl. Beat on a higher setting until smooth, then repeat with the rest of the icing sugar. Continue to beat for 1-2 minutes, until pale and fluffy.
Place a pan of water over a low heat. Bring to a gentle simmer and place a heatproof bowl over the top, making sure it doesn’t touch the water. Break up the white chocolate, add to the bowl and let it slowly melt. Stir gently once or twice. When nearly all the chocolate has melted, remove from the heat and stir constantly until completely melted. Leave to cool slightly, then add to the buttercream and mix until combined and smooth. Turn the cooled loaf cake out of its tin, and cover the top and sides of the still-upturned loaf cake with the white chocolate buttercream. Transfer to the fridge to chill for 15 minutes.
Meanwhile, combine the ready mix royal icing with 80ml cold water in a deep bowl. Using an electric mixer or electric hand whisk, starting slowly and gradually increasing the speed, beat for about 5 minutes until standing in soft peaks. If the icing is too soft, beat in a little icing sugar, 1 tsp at a time. Add a few drops of water if it is too stiff. Set aside 2 tbsp royal icing, and evenly divide the remainder between 3 bowls. Colour one bowl of icing with 1 tsp red food colouring, another with the remaining 1 tsp red colouring and the third bowl with the pink colouring. Mix in 2 tsp icing sugar each to 1 bowl of red and the pink icing. This should thicken the icing and make it possible to pipe stripes on to the cake. If it isn’t thick enough, continue to add icing sugar until you have the consistency you want. Spoon the thickened red and pink icings into separate disposable piping bags, each fitted with a small round writing piping nozzle.
Pipe a heart outline on to the cooled heart biscuit using the thickened red icing. Spoon the slightly looser red royal icing into the middle, then leave to set.
Meanwhile, pipe alternate red- and pink-coloured stripes on to the sides of the cake, starting from the top of the cake and finishing at the base. Finish with a little squeeze to create a small blob at the bottom of each stripe. Brush the undersides of the mini blossom decorations with a little water and stick around the top edge of the cake, covering the start point of each of the piped stripes and overlapping slightly.
When the icing has set on the heart biscuit, pipe on a Valentine’s message using the 2 tbsp of set aside white royal icing. Arrange the iced biscuit heart on the cake. Decorate the top of the cake with the chocolate hearts and serve in slices so you can see the heart in the middle.