In a large pot, bring water to a boil.
Blanch the salmon so it firms up. I find that 2 to 3 min is good; some people opt to boil it for longer, while others don’t boil it at all. Remove the salmon and dry it well on paper towel.
Prep the onions, the salmon, and the pan with your sauce.
Layer the salmon and onions in the mason jars, being careful not to pack too tight. Be sure to leave room for liquid.
In a large saucepan bring the water, ketchup, vinegar, sugar, salt, peppercorns, bay leaves, and cloves to a boil.
Carefully pour the mixture into the jars, ensuring all contents are covered. Note: If you run low of the mixture you can top up with a little water, or just make more.
Rest the jars until they are room temperature. Seal the jars and refrigerate for 4 days.