1. Preheat oven to 325 degrees F. Line the bottom of a tube pan with waxed paper or parchment paper.
2. Whisk the flour, baking powder, and salt in a medium bowl and set aside.
3. In a small bowl or coffee cup, heat the vanilla in a microwave for 10 seconds. Stir in the instant coffee until partially dissolved. Set aside; coffee will dissolve completely while you prepare the rest of the cake.
4. Add egg whites and cream of tartar to a large bowl. Use an electric mixer onmedium speed to beat until frothy. Adjust the mixer to high and gradually add 1/3 cup of the sugar; continue to beat until thick and glossy, with stiff peaks, about 4 to 6 minutes longer. Scrape the beaten whites into another bowl and set aside.
5. In a separate large bowl, stir together the chocolate and cocoa. Pour boiling water over and stir until chocolate is melted and the mixture is smooth; set aside.
6. In the bowl used to beat the egg whites (no need to clean it), beat the egg yolks and the remaining 1 cup sugar at medium-high speed until thick and pale, about 1 minute. Stir the vanilla-coffee mixture until coffee is fully dissolved and add to the yolks with the water and beat to mix. With the motor running at medium speed, gradually add the oil and beat to mix. Add the mixed dry ingredients and whisk until just combined and smooth (do not over mix). Add aboutone quarter of the reserved egg whites and fold in until just combined. Add remaining whites and rapidly but gently fold into the batter until combined.
7. Add about half the batter to the bowl with the chocolate mixture and rapidlybut gently fold with a large flexible spatula to combine. It will deflate slightly,but this is OK.
8. Ladle the batters into the tube pan, alternating ladles of the vanilla and chocolate. Gently run a butter knife through the batter in the pan to swirl them. Smooth the top, and bake until golden brown and springy, about 50 minutes.
9. Remove the pan from the oven and invert it. If your pan does not have feet, place it on the neck of a sturdy bottle, or rest the lip of the pan on other pans or bowls, so air can circulate underneath. Cool to room temperature, at least 2 hours.
10. Run a knife around the tube and the edge of pan to loosen the cake, andinvert onto a serving plate. Remove paper liner from the bottom, then reinvert the cake onto the plate. Dust the cake with confectioners' sugar, if using. Slice with a serrated knife and serve with whipped cream and fresh berries, if desired. (Store leftover cake in an airtight container at room temperature up to 3 days.)
Source: Hannaford fresh Magazine, July - August 2011