Preheat oven to 350º.
To prepare soufflé cakes, lightly coat 8 (4-ounce) ramekins with cooking spray. Sprinkle each with 1 teaspoon sugar.
Combine 2/3 cup sugar and 1/2 cup water in a medium, heavy saucepan. Bring to a boil over medium heat, stirring to dissolve sugar. Remove from heat. Add chocolates, stirring with a whisk until chocolates melt. Combine 1/2 cup cocoa, 3 tablespoons cornstarch, and 1/8 teaspoon salt. Add cocoa mixture to chocolate mixture, stirring with a whisk. Whisk in 2 egg yolks and 1 teaspoon vanilla.
Place egg whites and cream of tartar in a large bowl; beat with a mixer at medium speed until soft peaks form. Gradually add 3 tablespoons sugar, 1 tablespoon at a time, beating at high speed until stiff peaks form. Gently stir one-fourth egg white mixture into chocolate mixture; fold in remaining egg white mixture. Spoon chocolate mixture into prepared ramekins. Place ramekins in a large baking dish; add hot water to dish to a depth of 3/4 inch.
Bake at 350º for 15 minutes or until puffy and slightly cracked. Remove ramekins from dish, and place on a wire rack.
To prepare crème anglaise, combine 3 egg yolks and 1/8 teaspoon salt in a medium bowl. Gradually add 1/3 cup sugar, whisking until thick and pale yellow (about 3 minutes).
Heat milk in a heavy saucepan over medium heat to 180° or until tiny bubbles form around edge (do not boil). Remove from heat.
Gradually add hot milk to egg yolk mixture, stirring with a whisk. Return egg yolk mixture to pan; cook over medium-low heat 5 minutes or until slightly thick and mixture coats the back of a spoon, stirring constantly (do not boil). Remove from heat. Stir in 2 teaspoons vanilla. Serve with soufflé cakes.
Note: A water bath tempers the heat and insulates the soufflés, ensuring a creamy texture. Line the baking dish with a towel to keep the ramekins in place.