Season the pork neck with ground pepper. Sear in a large pan over medium-high heat for 2–3 minutes per side until browned, without cooking through. Remove from pan and sprinkle with chopped thyme and rosemary. Soak the hay in water for 10 minutes, then line a baking sheet with the soaked hay. Place the pork neck on the hay and cover completely with the remaining hay.
In a clean bowl, beat the egg whites until soft peaks form. Gently fold in the salt to create a thick mixture. Spread this mixture evenly over the pork neck and hay in a 3–4 cm thick layer. Bake at 210°C / 410°F (190°C / 374°F fan-assisted) for 90 minutes, until the internal temperature reaches 63°C / 145°F.
Remove from oven and let rest for 5–10 minutes. Crack open and remove the salt crust and hay. Slice and serve.