1. Preheat oven to 350 degrees.

2. To prepare cake, lightly spoon flour into a dry measuring cup; level

with a knife. Combine flour, 3/4 cup sugar, and cinnamon, stirring with a

whisk, and set aside. Combine espresso and hot water, stirring until

espresso dissolves; set aside.

3. Place egg whites in a large bowl; beat with a mixer at high speed until

foamy. Add cream of tartar and 1/4 teaspoon salt; beat until soft peaks

form. Add 3/4 cup sugar, 2 tablespoons at a time, beating until stiff peaks

form.

4. Beat in espresso mixture and vanilla extract. Sift 1/4 cup flour mixture

over egg white mixture; fold in. Repeat procedure with remaining flour

mixture, 1/4 cup at a time.

5. Spoon batter into an ungreased 10-inch tube pan, spreading evenly. Break

air pockets by cutting through batter with a knife. Bake at 350 degrees

for 50 minutes or until cake springs back when lightly touched. Invert pan;

cool completely. Loosen cake from sides of pan using a narrow metal

spatula. Invert cake onto plate.

6. To prepare sauce, place egg yolks in a large bowl; set aside. Combine

1/2 cup sugar, cornstarch, and 1/8 teaspoon salt in a medium saucepan.

Gradually add 1/2 cup milk, stirring with a whisk until smooth. Stir in

remaining milk. Scrape seeds from vanilla bean into the milk mixture; add

bean to mixture. Heat milk mixture over medium heat to a boil. Remove from

heat; gradually add hot milk mixture to egg yolks, stirring constantly with

a whisk.

7. Return milk mixture to pan. Cook mixture over medium heat until thick

and bubbly (about 4 minutes), stirring constantly. Remove from heat. Spoon

milk mixture into a bowl; place bowl in a large ice-filled bowl for 10

minutes or until milk mixture comes to room temperature, stirring

occasionally. Remove bowl from ice; stir in liqueur. Cover and chill

completely.

8. Remove and discard vanilla bean. Serve angel food cake with sauce, and

sprinkle with toasted hazelnuts.