FOR THE CARAMEL: Heat 1 1/2 cup of the sugar and 1/2 cup of the water in a small, heavy-bottomed saucepan until the sugar dissolves. Cook over medium heat until the syrup turns a warm caramel color. Don't stir, just swirl it in the pan.
Turn off the heat, add 1/2 cup water and 1/2 teaspoons of the vanilla; be careful, the syrup will bubble violently.
Stir and cook over high heat until the caramel reaches 230 degrees F. (thread stage) on a candy thermometer. Set aside.
FOR THE PRALINE: Combine the almonds with 1/4 cup of the caramel and spread them on a sheet pan lined with parchment paper. Bake for 10 to 12 minutes, until the almonds are lightly browned.
Allow to cool at room temperature and then break up in pieces.
Lower the oven to 250°F Line 2 sheet pans with parchment paper.
FOR THE MERINGUES: Beat the egg whites, salt and cream of tartar in the bowl of an electric mixer fitted with the whisk attachment on medium speed until frothy.
Turn the mixer on high speed and add the remaining 1 cup of sugar. Beat until the egg whites are very stiff and glossy.
Whisk in the remaining teaspoon of vanilla. With dessert spoons place 12 mounds of meringue on parchment paper and bake for 20 minutes, or until a cake tester comes out clean.
FOR THE CREME ANGLAISE:
Beat the egg yolks and sugar in the bowl of an electric mixer fitted with the paddle attachment on medium-high speed for 3 minutes, or until very thick. Reduce to low speed, and add the cornstarch.
With the mixer still on low, slowly pour the hot milk into the eggs. Pour the custard mixture into a saucepan and cook over low heat, stirring constantly with a wooden spoon, until thickened. The custard will coat the spoon like heavy cream. Don't cook it above 180F or the eggs will scramble!
Pour the sauce through a fine strainer, add the vanilla extract, Cognac, and vanilla seeds, if using, and chill.
FOR SERVING: Pour creme anglaise on the bottom of individual plates. Place a meringue on top of each serving, drizzle with caramel sauce, sprinkle with praline, and serve.
To make a day or two ahead, leave the caramel and praline at room temperature and refrigerate the creme anglaise. Bake the meringues before guests arrive and assemble the desserts just before serving.