Preheat the oven to 400°F (200°C).

Season the lamb rack generously with salt and pepper.

In a small bowl, combine the chopped pistachios and fresh coriander.

Heat olive oil in a skillet over medium-high heat. Sear the lamb rack, fat side down, for about 3-4 minutes until browned. Turn and sear the other side for another 2-3 minutes.

Remove the lamb from the skillet and brush the Dijon mustard over the meat.

Press the pistachio and coriander mixture onto the mustard-coated lamb, ensuring an even crust.

Place the lamb rack on a baking sheet and roast in the preheated oven for 15-20 minutes for medium-rare, or until your desired doneness is reached.

While the lamb is roasting, prepare the caramelized fennel. In the same skillet used for the lamb, add the sliced fennel and sauté over medium heat until softened, about 5-7 minutes.

In a mixing bowl, combine the softened butter, honey, lemon zest, and lemon juice. Mix until smooth and creamy.

Once the fennel is caramelized, remove it from the heat and fold it into the compound butter mixture.

When the lamb is done, let it rest for 5-10 minutes before slicing. Serve with a generous dollop of the caramelized fennel compound butter on top.