Martha draws inspiration from kubaibat hayel, a popular Arabic dish of grape leaves stuffed with rice, vegetables, and spices, for this riff on stuffed cabbage. Roasted lamb chops make it special enough for company.
Make the lamb spice mix: In a medium saute pan, toast cumin, mustard, coriander, and fenugreek over medium heat until fragrant, 2 to 3 minutes. Transfer to a spice grinder along with peppercorns and pulse until roughly chopped; set aside.
Make the stuffed cabbage: Using a paring knife, remove center core of cabbage. In a large nonreactive stockpot, bring 2 quarts of salted water to a boil. Add cabbage and cook until outer leaves are bright green and tender, 2 to 3 minutes. Lift cabbage from water and remove outer leaves. Return cabbage to boiling water and repeat brief cooking and removal of leaves until all leaves are cooked. Trim thick center vein from bottom of each leaf. Reserve four large outer leaves to line bottom of pan.
In a medium skillet, melt 4 tablespoons butter over medium heat. Add onion and cook until golden and tender, about 8 minutes. Add 1 tablespoon reserved spice mix and a pinch each of saffron and salt. Cook until fragrant, about 2 minutes. Transfer onion mixture to a large bowl and add cooked rice, currants, pine nuts, and parsley. Season filling with salt and mix until well combined.
Add 1/4 cup filling to one cabbage leaf. Fold sides of cabbage over filling and tightly roll, starting with the stem end. Repeat with remaining leaves and filling.
Line a 5-quart Dutch oven with reserved outer leaves. Place potatoes in bottom of pot and top with stuffed cabbage leaves, tucking tomatoes between them. Season with salt, pepper, and a pinch of saffron.
In a medium saucepan, melt remaining 4 tablespoons butter over medium heat. Add tomato paste and cook, stirring, for 2 minutes. Add chicken stock along with sugar and remaining pinch of saffron. Season with salt.
Pour tomato paste mixture over stuffed cabbage and bring to a boil. Reduce to a simmer, cover, and cook until cabbage is very tender, about 1 1/2 to 2 hours.
Make the rack of lamb: Preheat oven to 375 degrees. Season lamb all over with salt and 4 tablespoons reserved spice mixture (1 tablespoon per side), rubbing to evenly coat meat.
Heat oil in a large ovenproof skillet over medium and sear lamb, meat-side down, until golden and crisp, 3 to 5 minutes. Turn lamb and transfer skillet to oven. Roast lamb until a thermometer inserted in center reaches 130 degrees (medium-rare). Let rest 5 minutes before carving lamb into individual chops.
To serve, place stuffed cabbage, along with potatoes and sauce, on a serving platter, and top with lamb. Garnish with mint.