In a saucepan over medium heat, whisk together maple sugar, vinegar, water and ketchup until maple sugar is melted.

Mix arrowroot powder and water together to make a slurry and pour it into the sauce. Bring to a boil while whisking and allow the sauce to thicken - this will happen in a couple of minutes.

Once thickened, pour in a bowl and let cool.

Store in the refrigerator until ready to use.