You can use a combination of dry chickpeas and fava beans, or all dry chickpeas. Begin making the falafel a day in advance to soak the beans overnight. Make the tahini sauce in advance up to three days. An ice cream scoop works great as an alternative to a falafel scoop. Be careful not to make the falafel too large, or they won’t cook through to the center.
In a medium bowl, cover the chickpeas and fava beans with cool water by several inches. Soak them overnight and up to 24 hours.
Drain the chickpeas and fava beans. In the food processor, process them with a teaspoon of salt until they are ground to a coarse crumb. Add the mint, parsley, cilantro, jalepneo, garlic, onion, and sesame seeds and pulse until everything is finely ground and the mixture is a fine, web crumb—but not pureed. Transfer the mixture to a bowl, stir in the baking soda, and chill for at least 30 minutes and up to one day.
To make the tahini sauce, process the yogurt, tahini, salt, and garlic until combined. Pour in the lemon juice and pulse to combine. Taste and adjust the seasonings so that the sauce has a nutty flavor of tahini with a bit of the tang of the yogurt.
Heat the oil in a 2-quart saucepan or sauté pan until a pinch of herb dropped in floats and bubbles dramatically. Using an ice cream scoop or a large spoon, pack the falafel mixture tightly in to the scoop to form 2-inch ovals, and fry a few at a time until they are golden brown, flipping them over with tongs as soon as they are browned on one side. Remove the falafel from the oil with the tongs to a paper towel-lined plate, and fry the remaining falafel in the same way.
Serve the falafel hot with the tahini sauce on the side or drizzled over top.