01 -
Mix mustard, soy sauce, garlic, dried herbs, and ginger in a bowl. Gradually whisk in olive oil until emulsified to a mayo-like consistency. Coat lamb thoroughly with mixture. Place on rack (fat side up) in roasting pan and let sit at room temperature for 2 hours.
02 -
Preheat oven to 425°F. Scatter onion, lemon slices, and fresh herbs under rack in roasting pan.
03 -
Roast lamb for 30 minutes at 425°F.
04 -
Reduce oven temperature to 350°F. Continue roasting until lamb reaches desired doneness: about 135°F for medium-rare or 145°F for medium (approximately 1½ hours more). After 1 hour, pour 2 cups chicken stock into pan, adding more after another ½ hour if needed.
05 -
Remove roast from oven 5 degrees short of target temperature. Transfer to cutting board, tent with foil, and let rest 20-30 minutes.
06 -
Strain and de-fat pan juices into measuring cup. Add chicken stock if needed to make 2 cups. Mix flour and water to create slurry. Heat roasting pan over high heat, deglaze with wine, and reduce by half. Add reserved juices and whisk. Gradually add slurry, whisking constantly. Simmer until thickened, 5-10 minutes. Season with salt and pepper.
07 -
Remove netting/string from roast. Carve into slices and serve with gravy.