1. Several pounds of fresh-caught whole mackerel.
2. Nine times, by weight, of kosher salt as the weight of the fish.
Split each fish lengthwise, and do not remove the entrails. Place the fish in large bucket, and cover it entirely with the kosher salt. Leave the bucket outside in the sun to ferment for nine months, stirring weekly. After that time, strain and filter the mixture to harvest the garum, which should be a translucent amber color.
Here's a sauce recipe using it:
1. 1-2 drops of garum
2. 1 Tbsp of lard
3. 2 cups of chopped shallots
4. 2 cups of chopped celery
5. 3 cups of chopped garlic
6. 1 Tbsp of cake flour
7. 1 tbsp each of rosemary, chives, and dill.
Saute the shallots, celery, and garlic in lard until lightly browned. Add the white wine, and reduce by half. Add the lard and cake flour, and thoroughly incorporate until the sauce has been appropriately thickened and no longer tastes like flour. Add the herbs, remove from heat, pour into sauce boat, add the garum, and drizzle over fish.