How to Make It
Brine the chicken In a very large bowl, whisk the water with the salt, honey and lemon juice until the salt dissolves. Add the halved lemons along with the thyme, sage, bay leaves and peppercorns. Submerge the chicken in the brine, cover and refrigerate overnight.
Make the fried chicken Preheat the oven to 300°. Put the foie gras terrine in a pie plate and bake until most of the fat is rendered and the foie gras is sizzling, about 15 minutes. Scrape the foie gras and any fat into a fine sieve set over a small saucepan. Press on the solids to extract as much of the fat as possible. Discard the solids or reserve for another use. Stir the parsley, chives, minced sage, thyme and rosemary into the foie gras fat. Keep warm.
Lower the oven temperature to 200°. Drain the chicken and pat dry. Scrape off any herbs or peppercorns stuck to the skin.
In a large bowl, beat the egg whites until very frothy. In another large bowl, whisk the matzo meal with the flour and a generous pinch each of salt and pepper. Dip the chicken pieces in the egg whites, letting the excess drip back into the bowl, then dredge in the flour mixture, pressing to help it adhere. Transfer the chicken to a large rimmed baking sheet lined with wax paper.
Set a rack on another large rimmed baking sheet. In a large, heavy saucepan, heat 2 inches of oil to 375°. Fry the chicken in 3 or 4 batches over moderate heat, turning occasionally, until browned and an instant-read thermometer inserted in the thickest part of each piece registers 160°, about 10 minutes. Transfer the chicken to the rack to drain; keep warm in the oven. Add the sage leaves and chiles to the hot oil and fry until crisp, 30 seconds to 1 minute. Transfer to paper towels to drain.
Transfer all of the fried chicken to a very large bowl. Add the warm foie gras mixture and toss to coat. Transfer to a large platter and garnish with the crispy sage and serranos. Serve right away.