Preheat the oven to 180ºC/fan 170ºC/350ºF gas mark 4.
Butter well a large heart-shaped tin, 23cm at its widest part, and line the base with baking parchment.
Sift the flour and baking powder into the bowl, then add the butter (in knobs), the eggs, sugar and vanilla. Beat together until thoroughly blended, taking care not to over-mix so you will have a light sponge.
Scrape the batter into the tin or tins and level the top and bake for 30–35 minutes. When a skewer inserted into the centre comes out clean, it is ready. Leave to cool slightly in the tin, then turn out on to a wire rack, remove the paper and allow to become completely cold.
Make the buttercream by beating the butter, icing sugar and vanilla for 5 minutes until really soft and fluffy. Add drops of the pink food colour. Any shade is fine: you can pick a baby pink, a medium or, as we did for this photograph, a strong, full-on girlie tone.
Turn the cake upside down, split it horizontally and, using a palette knife, spread some of the pink buttercream over the cut surface, then add a layer of jam. Place the other half of the cake on top and spread the rest of the buttercream all over the top and sides, making it as smooth as possible.
Straight away, press a collar of the dragees all around the outside edge (the icing will start to set if you leave it) and sprinkle them all with a little glitter. Finish by placing the candles on the cake, if you like.