In a large bowl, whisk eggs well. Add chicken fat, oil, sea salt, chopped herbs and the seltzer. Mix to incorporate all. Add the matzo meal. Stir with a rubber spatula until well mixed. Cover with plastic wrap, refrigerate for 30 minutes, until firm and cold.
Fill a large pot with 6 quarts of water, and bring to a boil. Season with a bit of salt.
Lay a piece of waxed paper on your work surface, will hold 14 matzo balls. Using a spoon, or a 2″ cookie scoop, (as I do) –Oil hands with chicken fat or oil. Scoop a mound of the mixture (the size of a large walnut), add to the palms of your hands, and gently roll into a round ball. Place on the waxed paper. Repeat to make 14 balls. Adding more fat to your hands when necessary.
Make some mini sized ones if you like: Scoop out a portion, cut into thirds and roll. Cook these separately for 15 minutes until light and cooked through.
Drop the balls into the boiling water and cover the pot. Cook at a boil, but a little lower than a full boil. Keep covered (I shake the pot while it cooks – be careful of the boiling water.)
Cook for 30 minutes, can test one until it is fluffy, and cooked through. If slightly underdone, turn the heat off. The matzo balls will sink to the bottom and continue to poach for a few minutes.For denser matzo balls, cook 5 minutes less. Lift each ball out next to the sink, with a slotted spoon and drop the cooked balls into a large pan of cold water. When cool, drain water. Add the matzo balls to your warm broth. Can store the cooled matzo balls in the refrigerator a day or two ahead, being careful not to crowd them.