Leave a little of the red flesh (a very thin layer) when removing the flesh. Then peel off the green outer skin so only the white and pink rind is left. Chop this into small pieces. A medium watermelon should give you about 4 cups of chopped rind pieces.

Put the chopped rind, the orange zest and juice, grated ginger, juice of the limes and 1 cup water into a thick bottomed and largish pot. Bring to a boil and turn down the heat. Drop the halves of the orange (and the limes if you’re using them) into the pot. Let the mixture simmer until the rind is cooked and the liquid has reduced to about 1/4 cup.

Remove the orange and lime skins. Mix in the sugar, the allspice powder and the salt. Let it cook and the mixture thicken a bit. Stir in the butter and take the pot off the stove.

Let it cool. Transfer to sterile glass jars.