Step 1Soak the prunes in the tea overnight so that they swell up.
Step 2The following day, drain the prunes, discarding the tea. Roll each prune in paper towels to dry well. Place them in a sterilized 1 1/2 -quart wide-mouth canning jar.
Step 3Make a syrup with the sugar and one-half cup water; bring to a boil, stirring. Boil undisturbed for 2 minutes. Remove from the heat and allow to cool. Pour the syrup over the prunes. Completely cover the prunes with Armagnac; stir. If the prunes rise above the line of liquid, add more Armagnac. Let the prunes soak a minimum of 2 weeks in a cool, dark place or in the refrigerator. Use clean wooden tongs or a wooden spoon to remove the prunes as needed (keeps up to one year).
Step 1A day before serving, in a heavy enameled saucepan, scald the milk with the vanilla bean; set aside, covered, to keep warm.
Step 2In a mixing bowl, beat the egg yolks and sugar together until thick and pale and a ribbon forms when the whisk is lifted. Whisk in a pinch of salt.
Step 3In a heavy enameled or stainless steel saucepan, warm the beaten eggs and sugar over very low heat, stirring constantly. Gradually stir in the hot milk. Cook over low heat, stirring constantly with a wooden spoon, until the custard thickens enough to coat the back of the spoon, the froth on the surface has disappeared, and the custard registers about 165 degrees on a candy thermometer. Do not boil. Immediately remove from the heat.
Step 4Strain the custard into a chilled mixing bowl set over ice. Cool down quickly, stirring constantly. If using vanilla extract, stir it in at this point. Pour into an ice cream maker and freeze according to the manufacturer's instructions.
Step 5Meanwhile, coarsely chop the prunes with a large sharp knife or by pulsing in a food processor. When the ice cream is half frozen, add the prunes and the Armagnac syrup. When almost frozen, add the cream. When the ice cream is done, transfer it to an airtight container and set in the freezer overnight.
Step 6To serve, place a whole, soaked prune on top of each portion and drizzle with a teaspoon or so of the syrup.