For the ice cream: Pour the chilled vanilla custard into an ice cream maker and churn until thick but still just soft. At this point, add the double cream, the armagnac, diced prunes and their syrup. Continue to churn until thick, then transfer to a container and freeze until ready to use.
For the fois gras: Reduce the veal or poultry stock down by 1/2 or until it obtains sauce consistency. Clean the foie gras and remove the veins. Cut the lobe into 2-ounce medallions and score the surface of the foie gras in an "x" pattern. Season the medallions with salt and pepper and sear in a very hot pan until medium rare.
Slice the pineapple into 1/8-inch thick slices. Remove the core and sprinkle the pineapple with the white sugar. Saute the pineapple in a minimal amount of oil until the pineapple is golden brown. For presentation, place the pineapple ring in the middle of the plate. Next, place a wedge of waffle on the pineapple ring then the foie gras on top of that. Finish off with a scoop of the ice cream and chervil sprig. Drizzle a little of the veal reduction around the plate and serve.
Bring the milk to a boil. Split half a pod of vanilla, scraping out all the seeds into the milk. Whisk the egg yolks and sugar together until thick. Pour the milk over, whisking continuously. Return to the pan and cook over gentle heat, stirring with a wooden spoon until the custard thickens enough to coat the back of the spoon. Pass through a fine conical sieve. Serve hot or cold.
Boil 3 pints water in a saucepan. Remove from heat and add the tea bags. Leave to infuse for 2 minutes, then add the prunes. Cover the pan. Make a syrup with the sugar and 4 ounces water, bring to a boil, leave to cool and refrigerate.
The following day, strain the prunes and put them in a large glass jar, pouring the armagnac over. Add the cold syrup. Leave to macerate for a month in a cool place.
Sift together the dry ingredients. Slowly whisk in the yolks, 1 at a time. Next, add the milk followed by the melted butter. After the egg whites have been whipped to soft peaks fold them into the batter. Finally add the chopped rosemary and the batter is ready for use in a waffle iron.