Please read the notes regarding the antlers - they are fragile little things.
Grease a 30x20cm swiss roll tin and line with baking parchment
Put the butter and marshmallows into a medium saucepan and place over a moderate heat to melt the ingredients. Stir often with a wooden spoon to prevent the mix from burning. Stir until smooth
Tip the cocoa powder and rice krispies into the pan and stir until completely coated
Spoon the mix over the parchment and flatten out, pressing firmly, to reach the sides of the pan. Ensure the top is as smooth as possible. I find using a piece of cellophane is the ideal way to do this task without getting into a sticky mess
Set aside for 20 minutes to firm up
Cut circles out using cookie cutters. I used a 7cm cutter to get 10 circles and a 5 1/2 cm cutter to squeeze out a further 2. Ensure you cut right up to the edge of the pan to get the maximum amount of treats. Exact cookie cutter size will affect how many shapes you can cut
Melt the chocolate, put into a piping bag fitted with a round piping tip (I used this one) and pipe out pairs of antlers approx 3.5 cm long and 3-4mm wide. (I drew lines onto parchment and then turned it over to use as a guide to ensure the antlers were of similar length. I recommend you pipe a few extra pairs since the antlers are fragile, so breakages will happen. Scatter with the coconut and let set completely
When ready to decorate the Krispie treats remelt the remaining chocolate and use to dab the backs of the candy eyes and red sweets before attaching to the treats.The chocolate will set and act like glue
Also use a little melted chocolate to attach the antlers to the tops of the reindeer faces
Store the Krispie Treats on parchment in an airtight container. Take great care when putting the treats into the tin and taking them out as those antlers are prone to breaking easily. Do not put the reindeer too close to each other. (see notes)
The antlers are very fragile. For this reason, I recommend piping out numerous spare antlers at the outset (5 pairs). I also do not recommend that you make these Rudolph Chocolate Rice Krispie Treats to take to another venue. Really, these beauties need to be handled with the utmost of care. Being jiggled about en-route to a party will lead to antler issues.
If you are set on taking these along to a gathering, I would swap the dainty chocolate antlers for some mini pretzels. These can still be dipped in chocolate and dusted in coconut and will hold up far better on sleigh rides (or car rides). They may not be quite as refined, but they will look far better than a bunch of antlerless Rudolphs who look as though they have been fighting in the storage tin.
Any leftover chocolate can be used to make a hot chocolate