Pre-heat oven to 325° (160°C). Place oven rack to the lowest position.
In large bowl, whisk together flour, sugar, cocoa, baking powder and salt. Add water, oil, vanilla and egg yolks; beat with electric mixer until smooth. Set aside.
In separate large bowl, with clean beaters, beat egg whites and cream of tartar on high speed until stiff peaks form, about 2 minutes. Fold one-quarter of egg white mixture into egg yolk mixture. Fold in remaining egg whites until no streams remain. Scrape into ungreased 10-inch (25 cm) tube pan. Run spatula through batter to eliminate any air bubbles; smooth top.
Bake until cake springs back when lightly touched, about 75 minutes. Turn pan upside down and let hang on legs attached to pan or on a bottle, until completely cooled, about 2 hours. Loosen side of cake with knife or metal spatula and remove from pan. Turn out, bottom side up, onto cake plate.
Chocolate Glaze: In small microwave-safe bowl, combine chocolate chips, cream and butter. Microwave on medium (50% power) for 1½ to 2 minutes stirring once, or until mixture is melted and smooth. Spread over the top of cooled cake, allowing to drip down the sides.
Let set before serving.
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