Brine the Meat: Whisk the cold buttermilk with a heavy dash of hot sauce and salt in a large bowl. Submerge your whole, unsliced chicken breasts completely, cover tightly, and rest in the refrigerator for exactly 4 hours to deeply tenderize.
Build the Breading: Whisk your flour, cornstarch, and heavy spices together in a shallow dish. Drizzle exactly 2 tablespoons of the wet buttermilk brine directly into the dry powder, mixing with a fork to create tiny, textured clumps.
Coat the Breasts: Pull your wet, unsliced chicken straight out of the brine, letting the excess drip off. Press the massive pieces firmly into the clumped flour, packing the dry powder deeply into every crevice for a craggy crust.
Fry the Chicken: Heat a heavy quart of peanut oil in a deep cast-iron skillet until it hits 350°F (175°C). Drop the breaded meat into the hot fat, frying untouched for 8 minutes per side until deeply golden and crispy.
Soak the Bread: Whisk the raw eggs, heavy cream, white sugar, and vanilla extract vigorously inside a large bowl. Drop your thick-cut brioche slices into the sweet custard, letting them soak for exactly 10 seconds on each side.
Sear and Assemble: Melt butter in a clean skillet, searing the wet bread until a deeply caramelized crust forms. Build the sandwich by placing the huge, crispy chicken breast between two hot slices, dripping thick maple syrup generously over the top!