- One 8-rib rack of lamb, Frenched
- 1 Teaspoon kosher salt, plus more for the lamb
- 1/4 Teaspoon black pepper, plus more for the lamb
- 2 Tablespoons olive oil
- 5 Tablespoons unsalted butter, room temperature
- 1/2 Cup breadcrumbs
- 1/4 Cup finely ground pistachio nuts
- 1 Tablespoon Dijon mustard
Season the lamb generously with salt and pepper. Place a heavy skillet over high heat and add the olive oil. When the oil begins to smoke, place the lamb fat side down in the skillet and sear until deeply colored. Stand the rack up to brown its top, then roll over to brown the bone side. Remove from the pan and cool on a rack.
Place the butter, salt, and pepper in a bowl; beat with an electric mixer until light and fluffy. Add the breadcrumbs and pistachios. Stir the mixture with a wooden spoon to combine well and form a ball. Transfer to a sheet of waxed or parchment paper; place another piece of waxed paper on top. Press the ball flat between the sheets of paper. Roll out the mixture 1⁄8-inch thick with a rolling pin. Keeping the rolled mixture flat, freeze at least 10 minutes, or up to 2 weeks if tightly covered.
Preheat the oven to 450 degrees. Put a rack on the top shelf in the oven.
Twenty-five minutes before serving, remove the butter mixture from the freezer and cut a rectangular shape from it the same size as the fat side of the rack. Brush the fat side of the rack with the Dijon mustard. Remove the paper from one side of the cut piece of frozen butter crust. Press the crust onto the rack over the mustard, allowing your hands to warm it and shape it to the rack. The mustard will act like a delicious glue, helping to hold the buttery crust in place. Remove the remaining piece of paper.
Place the lamb crust side up on an aluminum foil-lined baking sheet. Roast until a thermometer inserted into the center (NOT through the crust!) reads 125 degrees, 12 to 14 minutes. Remove and rest on a rack for 8 minutes before carving to serve. Unused pieces of the crust can be put together and rerolled to be used again. Store unused portions tightly covered in the refrigerator.