Along with the nut loaf and the veggie lasagne, veggie burgers have long been the butt of anti-vegetarian jokes. These have also been the claggy, yet somehow throat-stickingly dry, offerings of unimaginative restaurants attempting to cater for their non flesh-eating patrons. For years vegetarians ate these sad excuses for meals: nut loaves that disintegrated on the fork, requiring mashing up with …