Step 1 Prepare the pistachio paste: In an oven heated to 350 degrees, toast the pistachios until fragrant, 6 to 8 minutes. Remove and cover with a towel, rolling to remove the skins from the hot pistachios. Grind the hot pistachios in a food processor until they are reduced to a paste. This should make about 2 1/2 tablespoons paste. Set aside.
Step 2 Reduce the oven temperature to 325 degrees. Bring a large saucepan of water to a boil.
Step 3In a heavy-bottomed saucepan, combine the cream, one-fourth cup sugar and vanilla seeds. Bring the cream just to a simmer, being careful that it does boil.
Step 4Meanwhile, whisk the remaining sugar with the egg yolks. Slowly add the hot cream mixture to the yolks, whisking constantly, to temper. Whisk in the pistachio compound to taste; depending on the intensity of the nuts, you might not use all of the paste (we tested with all of the paste).
Step 5Strain the base to remove any lumps, then divide it among 6 (4-ounce) ramekins. Place the ramekins in a baking pan and slide the pan onto the center rack of the oven. Add enough boiling water to the pan to come halfway up the ramekins.
Step 6Loosely cover the pan with foil and bake the custards for 18 minutes. Check the custard by gently shaking the pan; if it jiggles gently (as with barely set gelatin), it is set. Otherwise, continue to bake, checking every 2 to 3 minutes until the custards are set, 5 to 10 minutes or more.
Step 7When the custards are set, gently remove the baking pan from the oven, uncover the custards and cool them (still in the pan) to room temperature. Remove the cooled custards from the baking pan and refrigerate until well chilled, at least 2 hours.
Step 8Before serving, remove the chilled custards and sprinkle a scant teaspoon of sugar over the surface of each, spreading the sugar with the back of a spoon to evenly cover the top.
Step 9Use a small torch to caramelize the tops of each of the custards. Alternatively, place the ramekins on a baking sheet and place under the broiler just until the sugar melts and caramelizes, 1 to 2 minutes.