Into a bowl, sift together the flour, baking powder, soda, and salt. In another bowl with an electric mixer, cream the butter, and add the sugar gradually, beating, and beat the mixture until it is light and fluffy. Add the eggs, one at a time, beating well after each. Beat in the vanilla. Add the flour mixture alternately with the sour cream, beginning and ending with flour, and blending the batter after each addition. Transfer about a third of the batter to another bowl and stir in the espresso mixture, stirring until the batter is well combined. Spoon half the plain batter into a well-buttered 8-inch bundt pan, spreading it evenly. Spoon the coffee batter over the plain, spreading it evenly and spoon the remaining plain batter on top, spreading it evenly. Bake the cake in the middle of a preheated 350f oven for 55-60 minutes, or until it is golden and a tester comes out clean. Let it cool in the pan on a rack for 30 minutes. Invert the cake onto the rack and let it cool completely. In a bowl, stir together 2 Tbsp of brewed coffee and the espresso powder, stirring until the powder has dissolved. Sift the conf. sugar and add it, stirring until it is combined well. If necessary, add more coffee to obtain a pourable consistency. Pour the glaze over the coffeecake and let the cake stand for 10 minutes or until the glaze has set. Serve warm. a 1989 Gourmet Mag. favorite