Place oven rack in lowest position. Preheat oven to 325°. Combine flour, sugar and salt. Whisk egg yolks, water, lemon juice and vanilla; add to flour mixture. Beat until blended.
Beat egg whites and cream of tartar until soft peaks form; fold into batter. Spoon into an ungreased 10-in. tube pan. Cut through batter with a knife to remove air pockets. Bake 50-60 minutes or until top springs back when touched. Immediately invert pan; cool completely.
For topping, grease a 15x10x1-in. pan. In a heavy saucepan, combine sugar, corn syrup, water and coffee granules. Bring to a boil, stirring constantly. Cook, without stirring, until a candy thermometer reads 300° (hard-crack stage).
Remove from heat; stir in baking soda. Immediately pour into prepared pan. Stretch brittle in pan with two forks; cool. Break into pieces. In a large bowl, beat cream until it begins to thicken. Add sugar and vanilla; beat until stiff peaks form.
Unmold cake; cut horizontally into four layers. Place bottom layer on a serving plate; top with 1/2 cup whipped cream. Repeat layers twice; top with remaining layer. Frost top and sides of cake with remaining cream. Sprinkle with brittle. Yield: 12 servings.