Sterilize the jar with the lid in the oven: place the jar with the lid in a preheated oven at 110C for 20 minutes.
Cut cucumbers into slices, chop dill and garlic. Put everything in a bowl, add spices and mustard. Pour boiling water over and leave to marinate for 3 hours. Stir the cucumbers every 30 minutes.
Pour the mixture into a sterilized jar and close.