To make the soufflé base

Whisk together the egg yolks and sugar in a stainless steel bowl. Stir the flour and the salt into the egg mixture.

Bring to a boil a pot of water that is large enough to hold the stainless steel bowl so that it sits halfway down in the pot.

Scald the milk with the vanilla bean in a heavy-bottomed saucepot. Whisk the milk into the egg mixture.

Put the bowl over the pot of simmering water and cook the soufflé base, whisking constantly, for a couple of minutes, until the mixture thickens. Whisk until smooth. Remove from the stove and cover the base with plastic wrap directly on the surface to prevent a skin from forming. Refrigerate until cold.

Preheat the oven to 350 degrees.

Butter and sugar the inside of the soufflé dish with the 1 tablespoon of butter and the 2 tablespoons of sugar.

Put the egg whites in the bowl of an electric mixer. With the whisk attachment, whip them on medium speed until foamy. Add the cream of tartar and salt. Increase to high speed and continue whipping until stiff but not dry. Stir the praline into the vanilla base. Fold in the whites.

Carefully spread the batter in the prepared dish and gently tap the dish on the counter. Bake the soufflé for about 30 to 35 minutes, until golden brown and firm around the edges.

Dust the soufflé with powdered sugar and immediately serve with chocolate custard sauce.