Trim the tops of the cake layers to level them (a cake wire is best for this) then place one layer on a serving platter or board.
Spread over a thin layer of the buttercream then pipe a wide ring of buttercream around the edge of the cake. You can also add a blob in the middle to help make the cake more sturdy (I didn't do this but in hindsight I should have done!).
Spread a couple of spoonfuls of lemon curd inside the ring of buttercream, making sure not to overfill it.
Spread a thin layer of buttercream over the bottom of one of the remaining cake layers and place it on top. Repeat the same steps as before.
Spread a thin layer of buttercream over the TOP of the final cake layer and place it on the cake upside down to give you a flat surface.
Spread a layer of buttercream over the top and sides of the cake, use a bench scraper or palette knife to get the sides smooth but leave the top rough so it looks snowy.
Cut a slit in the top of the cake where you want each of the trees to go and press a tree trunk into each one. Insert a wooden skewer into the cake close behind each tree to hold them up. (You will probably need to trim the skewers a bit to get the right height but make sure that they will go all the way through the cake and leave enough sticking out to hold the trees up.)
Use blobs of any leftover frosting to stick animal biscuits around the cake and place one on top of the cake (I just leant my fox against one of the trees).
Add sugared cranberries, sprigs of rosemary, hazelnuts, pecans and pumpkin seeds to complete the look.
Best served the day it is assembled but any leftovers will keep in an airtight container for up to five days.