In a large pot, melt together the chocolates, butter, and Lyle’s syrup. melt over low heat until completely melted and smooth.
Put the shortbread in a plastic bag and crumble into chunks. You want to keep some bigger pieces, you do not want to crush it entirely.
Add the shortbread, walnuts, cherries, and marshmallows.
Toss the until the chocolate covers everything.
Pour out the mixture into a tin foil lined pan.
Spread the mixture out evenly. Put in the fridge to set up, about 1 hour.
Pull the fudge out of the pan and cut into squares. This fudge is very rich, you can easily get 24 squares, if not more.
Using a strainer, dust a little powdered sugar snow on top of the fudge.