Transfer to a blender jar and blend until you get a smooth mixture.
Cook over medium-low heat, stirring occasionally.
Add the remaining ingredients and cook until the mixture thickens. This should take about 15-40 minutes.
Remove from heat, cool and store for later.
Notes
Use a thick, heavy bottomed pot to cook down the watermelon syrup. This will ensure even cooking.
If you spot any foaming on the surface of the watermelon syrup while it is cooking, use a spoon to gently skim it off.
I like that slight grainy texture, but if you love a smoother consistency, you can choose to strain the watermelon honey once it has cooled down.
I cooked the mixture for just around 15 minutes to get it to this consistency. If you prefer that sticky, saucy texture, you'll need to cook it down further- for about 30-40 minutes.
If you're doing this, make sure you keep stirring every minute or so during the final 10 minutes to prevent the sugars from burning.