Okay. This may sound less appealing than Best Velveeta Recipe or Most Ingenious Way to Disguise Mystery Meat. No surprise that a table of guests resoundingly declined to sample it recently at Babbo, despite an enthusiastic recommendation from the manager. Still, asked to send out an assortment of appetizers, chef Mario Batali included a dish listed on the menu as “Testa with waxy potatoes and thyme vinaigrette.” It looked like pounded carpaccio with shards of potatoes mashed in. Scooped and spread on bread, it went down like the best spicy steak tartare you ever had. One person at the table had to know and begged the manager to tell him the recipe. “Certainly,” said the waiter. “You start with head cheese …”