DAY 1: Combine ingredients and soak 2-3 days.
Measure ingredients into a large jar, screw on lid and shake to combine. Refrigerate 2-3 days until mustard seeds have expanded. NOTE: If you are short on time, you can combine ingredients, heat to a boil in a small pan, then cover and leave for 2-3 hours before continuing with the next step.
Prepare jars.
Cover jars with water and bring to a boil, boiling for 10 minutes. Once the time is up, turn the heat off and leave jars in the hot water until ready to fill.
Pulse mustard in food processor until thick.
Pour bowl of mustard mixture into your food processor, pulse until seeds start to split and mixture thickens. This only takes a few moments. Loosen with a little water if required. If mixture needs thickening, add extra mustard powder.
Prepare lids.
Place lids into a bowl of boiled water. Remove the lids from the water when you are ready to place them onto the jars to seal.
Ladle mustard into hot jars.
Pack mustard into hot jars, leaving 1/4 inch (0.5cm) headspace. Remove bubbles, check headspace is correct, and wipe rims with damp paper towel and seal.
Process jars in a boiling water canner for 15 minutes.
Process jars in a boiling water bath canner for 15 minutes (start timer once water returns to a full boil). When time is up, turn heat off and rest jars in water for 5 minutes before placing onto a towel-covered bench overnight to cool.
Next day: check for seals.
Check jars have sealed before labelling and storing in a cool, dry and dark place for up to 12 months. Jar lids should not flex up or down when pressed.
Note
Processing: Boiling Water Canner for 15 minutes
Storage: 12 months+
Allow to rest for 6-8 weeks to mellow the flavors, then enjoy this mustard on roast beef and other rich foods.