Add the tomato paste and cook, stirring, for 1 minute. Add the beef broth, honey, saffron water and cayenne pepper and simmer over high heat until the sauce is slightly thickened, about 8 minutes. Add the minced dates and simmer over low heat, stirring occasionally, until they break down and the sauce is thick and glossy, about 15 minutes. Remove from the heat. Stir in the lemon juice and season the sauce with salt and black pepper. Reserve 1/2 cup of the date barbecue sauce for glazing the lamb.