Make a bain-marie by filling a pot with a little water. Rest a heatproof bowl on the rim of the pot, making sure that the water doesn’t touch the bottom of the bowl.
Cook on a low heat and when the water starts to simmer add the chocolate, butter, and golden syrup to the heatproof bowl and allow it to melt - when it’s nearly there, give it a quick stir and take it off the heat.
Stir the crushed pretzels in to the chocolate mixture.
Line a muffin tin with muffin cases - if you have the time, you can line each muffin case with 5 pretzels to form a little holder for the mixture. one on the base, and 4 walls, but this isn’t totally necessary, the mixture will hold on it’s own when set. A single pretzel on top is a fairly good compromise!
Fill the muffin cases with the chocolate mixture and allow to set in the fridge for at least 1 hour.