Max Miller made some, then followed it up three years later with a better recipe.

If you just want to buy it, asian fish sauce is pretty close, I personally prefer Golden Boy brand.

I believe the specific sauce they used was garum, and while there's no single recipe that can be called "the definitive garum," there are a lot of options available.

Couple things to keep in mind:

1. There is a reason Rome forbade the production of garum in parts of their cities.

2. Worcestershire sauce and Asian fish sauces are close enough and you can buy those in a store.

Max Miller of Tasting History details a method of making garum in one of his videos (https://youtu.be/5S7Bb0Qg-oE)

Noma, the restaurant/food lab of Michelin chef Rene Redzepi, has a few less-traditional garum recipes in their "guide to fermentation" cookbook (can buy or find copies online if you look hard enough). I've copied their recipe for beef garum below:

Beef Garum

Makes 1.5 liters

• 1 kilogram freshly ground lean beef
• 225 grams Pearl Barley Koji
• 800 grams water
• 240 grams non-iodized salt

Beef garum truly took off at Noma around the time we were serving beef ribs on the menu, and there were a lot of beef scraps around.With any ferment, your ingredients must be fresh and pristine to avoid the threat of spoilage or mold. This holds especially true when it comes to meat- or seafood-based ferments, and it remains the case even if you’re using meat scraps that might otherwise be thrown away. If it’s not fresh enough to eat, it’s not fresh enough to ferment. For this recipe, you can grind the beef yourself or ask a butcher to do it for you, but avoid ground beef that wasn’t ground fresh the same day you start your garum. Finally, Aspergillus oryzae–inoculated koji works fine for this process (it’s what we use at the restaurant), but Aspergillus sojae, mentioned in the Shoyu chapter, is especially well tailored for garum fermentation. A. sojae produces higher levels of protease than other strains, so it more effectively breaks down the beef, producing higher levels of glutamate and thus more umami.

Equipment Notes

Our garum is fermented at 60°C/140°F, so it will require a fermentation chamber (see “Building a Fermentation Chamber”) or large-capacity electric rice cooker or slow cooker. (For those who are devoted to historical authenticity, see “Classical Garum,” for instructions on fermenting garum at room temperature.) Otherwise, garum only needs a food-safe container to hold it. We use 30-liter brewer’s buckets for the large quantities we produce at the restaurant, but for this recipe, you only need a 3-liter container. Glass jars and classic ceramic fermenting crocks work great, too.

In-depth instructions

Place the beef, koji, water, and salt into the fermentation vessel of your choosing. Use a handheld blender or gloved hands to mix everything thoroughly. Scrape down the inner sides of the container, then cover the surface of the garum with a sheet of plastic wrap, making sure it comes into contact with the liquid and the sides of the container to create an airtight barrier. Cover the container with a lid, and screw it on slightly less than completely tight if it’s a screw cap or leave it slightly ajar in one corner if it’s a snap lid to allow a bit of gas to escape.

Move the garum into the fermentation chamber and set the temperature to 60°C/140°F. If you’re using an electric rice cooker or slow cooker, use a sushi mat or wire rack as a buffer between the bottom of the bowl and the fermentation vessel; set it to “keep warm.” (If the bowl of your slow cooker or rice cooker has a capacity that’s close to the total volume of the garum mixture, you can forgo the fermentation vessel and ferment the garum directly in the bowl of the cooker.)

Allow the garum to ferment for 10 weeks. It will separate as it ages, with the ground meat floating to the top like a raft and the liquid sitting at the bottom. The salt and heat should keep malevolent microbes away, but the beef fat will begin to degrade into free fatty acids that can take on musty flavors, which can come across as rancid. As a countermeasure, several times during the first week remove the lid and plastic wrap and use a clean spoon or ladle to scoop off as much fat as possible. Stir the garum and replace the coverings. After the first week, you’ll only need to skim and stir the mixture weekly. After 10 weeks, the beef garum should be dark brown with a roasted, nutty aroma and deep, meaty, rich flavor.

Strain the garum through a fine-mesh sieve, pressing out as much liquid as possible without allowing any solids to pass through. Then strain the liquid again through a sieve lined with cheesecloth. The solids can be reserved and added to misos or used as a seasoning. If there’s any fat resting on top of the liquid, skim it off using a ladle or spoon. Pour the liquid into bottles or another covered container. The garum is very stable and will keep well in the fridge for at least a month. You can also freeze it for longer storage without any negative effects, but note that because of the high salt content, it probably won’t freeze completely solid. Beef

Directions

1. Freshly ground lean beef, water, koji, and salt.

2. Mix all the ingredients in the fermentation vessel by hand or with a handheld blender.

3. Cover the garum with plastic wrap and a lid and ferment at 60°C/140°F.

4. Skim the fat from the garum several times during the first week, stirring each time and then covering the liquid and vessel again.

5. Ferment for 9 weeks more, skimming and stirring once a week.

6. Strain the garum and store, covered, in the refrigerator or freezer.