Oil a 25cm bundt tin and line with cling film, ensuring there are no gaps and the cling film comes up and over the sides of the tin. Lightly brush with more oil.
Spoon the biscuit cake mix into the prepared tin, pressing down firmly with the back of a spoon. Bring the cling film over the top of the cake, seal and press down firmly. Transfer to the fridge and chill until the cake is completely firm, about 4 hrs. Can be prepared up to one week in advance. When the cake is set, it will easily drop out of the tin with a sharp tap.
Next, make the holly biscuits. Heat the oven to 200C/180C fan/gas 6. Lightly knead the gingerbread dough and roll out onto a lightly dusted work surface. Stamp out 16-18 holly leaves using a holly-leaf-shaped biscuit cutter, re-rolling the dough as needed (you can use different sizes of biscuit cutters, if you like). Transfer the biscuits to a lined baking sheet, spacing them apart. Bake for 8 mins until golden, then transfer to a wire rack and leave to cool completely.
Divide the royal icing between two bowls and colour with the food colouring – one should be dark green, the other light. Fit a piping bag with a small round nozzle and fill with 2 tbsp of the light green icing. Repeat with a second piping bag and the darker icing. Thin the remaining icings in the bowls with just enough water to achieve a runny consistency – when you run a spoon through the bowls, the trail should settle on its own by the count of 10.
Using the icing in the piping bags, pipe the outlines of the holly leaves on the cooled biscuits. Use each colour for half the biscuits (you don’t need to use all of the icing). Fill a piping bag with one of the thinned icings, snip off the end, and use this to flood the gaps of half the biscuits (they should have a contrasting outline). If you like, smooth the icing into the gaps using a clean, fine, damp paintbrush. Repeat with the other thinned icing and remaining biscuits.
Use the remaining icing in the piping bags to pipe over the outlines and central vein so they stand out. Leave to set overnight. The biscuits can be made up to one month in advance and stored in a cake box or sealed plastic container lined with baking parchment.
Next, make the poinsettia flowers. Colour the 3 tbsp royal icing with the yellow food colouring gel, and the remainder with the red food colouring gel. Fit a piping bag with a leaf nozzle and fill with the red icing (the icing should be slightly stiff ). Line a chopping board with baking parchment and draw three 6cm circles on the parchment (you can use the bottom of a glass or a biscuit cutter as a guide). Flip the parchment over, then pipe three poinsettia petals as a triangle to fit within one of the circles. Pipe the next three petals between the first to create a six- petalled base flower. Repeat in the other circles so you have three separate flowers. Leave to set for 30 mins, then pipe a smaller set of six petals on top of the base flowers. Leave to set for another 30 mins.
Fit a piping bag with a small round nozzle and fill with the yellow icing. Pipe a series of dots into the centres of the poinsettias. Leave to dry completely – this may take up to two days, as the flowers are quite thick.
To assemble the wreath, knead and roll out the chocolate fondant icing onto a work surface lightly dusted with icing sugar until it’s large enough to cover the wreath. Use this to cover the wreath, then press into position and use a 5cm round cutter to remove the fondant from the middle of the wreath. Neaten and trim the edges.
Carefully transfer the wreath to a cake stand or board. Place the holly biscuits on top of the wreath to create a flat surface, using a little royal icing to fix them in place. Add more biscuits on top. Carefully remove the poinsettias from the baking parchment using a palette knife, then fix to the leaves using more royal icing. Finish by fixing the red sugar pearls to the wreath with royal icing. Will keep for up to two weeks in a cool place. Take the biscuits off and enjoy separately, then cut the cake into wedges.