I recommend using a 1 quart saucepan as it's narrow and deep, but just large enough to contain all the ingredients. This makes it easier to place the immersion blender in the saucepan and blend everything easily. If you use a wider saucepan, the mixture will be too shallow for the immersion blender and you will have to transfer it to another container that's deep enough for the blender. And since this is blueberry (that stains), who wants to go through the extra steps of transferring the sauce and possibly making a mess? And now you have another container to clean. I strongly recommend using a small saucepan. Or, you can just leave the ketchup chunky and not even use the immersion blender. It's all up to you!
Keyword blueberry, blueberry ketchup, ketchup, sauce, vegan,