For the buttercream filling, beat the butter, powdered sugar, and vanilla extract together until pale and creamy.
Spread the buttercream on the top of one of your prepared sponges. On the base of the other sponge, add the raspberry jam, using a hot butter knife to evenly spread.
Put the sponges together so the jam and buttercream sandwich together.
For the fondant topping, in a bowl add the fondant icing with the red food coloring and some of the water, adding more if needed to create a loose but thick consistency.
Pour the icing over the cake covering the top and sides.
Decorate the cake with the sugar decorations, gently pressing into the icing to stick. Do the same for the raspberries. Leave the cake to set before serving.