Step 1Trim about 1/2 inch from the ends of the asparagus. Lay the spears on a work surface and peel them with a sharp vegetable peeler, starting about 1 1/2 inches from the top and running evenly down the length of each spear. (Spears are brittle and can snap when peeled in midair.) Cook the asparagus in lightly salted water for about 20 minutes. Drain the asparagus and cool. Lightly extract water from the asparagus by patting it dry with paper towels. Cut it into pieces, then puree it with the pistachios in a food processor and pour the puree into a bowl. Whisk the yolks, then combine them with the puree; set aside.
Step 2Heat the oven to 250 degrees.
Step 3Bring the double cream, the seeds from the vanilla bean and the 6 tablespoons of sugar to a simmer in a saucepan. Gently pour the cream mixture over the puree. Strain and pour into 4 or 6 (1/2-cup ramekins.) Place the ramekins in a baking dish and fill it with enough water to come halfway up the sides of the ramekins. Bake until the centers are set, 1 hour. Cool. Just before serving, sprinkle each ramekin with 1 to 2 teaspoons of sugar and broil until the sugar is melted, 1 minute.