Draw a snowman template on a piece of thin cardboard. Do this by tracing around one circle/cookie cutter (approximately 3.5cm diameter) for the body, and overlapping with a smaller circle (approximately 2cm diameter) for the head. Cut the template out, then use a dark pen or pencil to trace 24 snowmen onto two large pieces of baking paper (to fit on large baking trays), leaving a few centimetres between each snowman. Flip the baking paper over (so pen/pencil doesn't transfer to macarons) and place on two large baking trays.
Sift Chelsea Icing Sugar and ground almonds three times through a coarse sieve into a medium jug/bowl. Set aside.
Place egg whites, vanilla extract and cream of tartar in a separate large, clean bowl. Beat with an electric mixer or stand mixer until soft peaks form. Add Chelsea Caster Sugar, a tablespoon at a time, beating until stiff, glossy peaks form (2-3 minutes).
In two batches, fold icing sugar/almond mixture into the egg white base. Continue folding the mixture just until you can drizzle the macaron batter off the end of your spatula in the form of a figure 8. The figure 8 should sink back into the mixture within about 10 seconds. Be careful not to under or over mix.
Transfer mixture to a large piping bag fitted with a small-medium round piping tip. Pipe two circles within each template on the prepared trays, with the circles just touching/overlapping (you don't want them to overlap too much, as the mixture will spread).
Bang trays on the bench a couple of times, to remove any points on top and get rid of air bubbles. You can pop any remaining bubbles on the surface with a toothpick. Leave on the bench for 30-60 minutes, until macarons form a crust/are no longer tacky on the surface.
Meanwhile, preheat oven to 155ºC bake (or 150ºC, if your oven doesn't have 5ºC increments). Bake macarons for 12-15 minutes. As they bake, they should form feet. They are done when the top of the macaron seems set and is no longer wobbly.
Leave to cool on trays. Carefully peel off the baking paper and store macaron shells in an airtight container (use baking paper between layers), until ready to assemble.
Bring cream to the boil in a small saucepan. Remove from heat, add chocolate and stir until smooth. Allow to cool.
Sandwich macarons together with white chocolate filling (you can spoon or pipe the filling on - we find piping quicker and easier). Flatten straws at the top and insert into the base of the snowmen (or use ice cream sticks instead).
Place egg white in a medium-large bowl and whisk vigorously with a fork until frothy. Sift in Chelsea Icing Sugar, then add lemon juice and mix with a spatula until you have a thick pipeable icing. Transfer three quarters of the mixture to a piping bag fitted with a small round piping tip. Tint remaining icing black with food colouring and transfer to a separate piping bag fitted with a small round piping tip.
Use the black icing to pipe eyes and mouths onto the snowmen. Affix orange sprinkles as noses and other colours as buttons, using the white icing as 'glue' (tweezers are helpful for placing the sprinkles). Pipe scarves onto snowmen using the white icing.
Once icing has set, tie colourful ribbons around the straws/sticks. Alternatively, encase each snowman in a small cellophane bag, with the opening of the bag at the base of the snowman. Tie closed with a ribbon.
Serve immediately or allow flavours to 'mature' by refrigerating for 12-24 hours. Any leftovers should be stored in an airtight container in the fridge and eaten within 5 days. Macarons can be dusted with Chelsea Icing Sugar for more of a snowy effect!