Measuring and prepping everything a head of time makes this a bit easier to deal with. Chop the onion and set in a small bowl. Measure out the horseradish and put in a small bowl, chop the peppers and garlic, add to the horseradish. Peel and wedge the lemon, removing as much of the white pith as possible, cut in chunks. Measure the spices in to a small bowl. Shell the tamarind if using whole.
You need a 6qt or so, non-reactive pot. Heat that up over medium-high heat and open the anchovies. The anchovies typically come in a 2 oz tin, packed in olive oil. You want the flat packed, not the ones rolled around capers.
Drain the oil from them in to the pot and when it gets to the point that it’s starting to smoke, toss in the chopped onions and cook those for a couple minutes before adding the horseradish, jalapeño, and garlic. Cook this for about a minute or so.
At this point, you pretty much add everything else… the liquids and spices. You can use all white vinegar if you want… but I saw a couple recipes that mentioned apple cider vinegar, so I thought I would use a bit of it to see how it went. A quick tip – measure the molasses first, then do a cup of the water, heating it in the microwave for about 30-60 seconds. This heats the molasses up and it comes clean from the cup easier than trying to scrape it out. Repeat for the corn syrup using the other cup of water needed.
Bring this to a boil, then turn down to a low to medium heat and simmer for about 2.5 to 3 hours, stirring occasionally. You are looking to reduce the liquid to about a third of it’s original volume, and it should nicely coat the back of a spoon dipped in to it.
Put a colander over a large bowl and carefully pour the contents of the pot in to filter out the larger pieces, transfer back to the pot and then repeat, this time using a fine mesh strainer. You may have to use the back of a spoon to press as much liquid through the strainer as possible.
Once cooled, transfer to a nice clean bottle or jar. I have an old Frank’s Hot Sauce bottle that is just right. It’s a 20 oz bottle and this recipe usually fills it up perfectly.