Preheat an oven to 350 degrees F (175 degrees C). Grease a 9-inch springform pan with 3-inch high sides. Wrap bottom of pan securely with aluminum foil so it comes up about 1-inch on the sides. Set aside.
Melt the chocolate chips with the instant coffee granules and water in a microwave-safe glass or ceramic bowl in 30-second intervals, stirring after each melting, for 1 to 3 minutes (depending on your microwave). Do not overheat or chocolate will scorch. Set aside to cool.
Beat the butter, margarine, and white sugar with an electric mixer in a large bowl until light and fluffy. The mixture should be noticeably lighter in color.
Add the room-temperature egg yolks one at a time, allowing each egg yolk to blend into the butter mixture before adding the next.
Pour in the flour gradually, mixing until just incorporated. Fold in the melted chocolate; mixing just enough to evenly combine.
Beat egg whites until foamy in a large glass or metal mixing bowl. Continuing to beat until stiff peaks form. Lift your beater or whisk straight up: the egg whites should form a sharp peak that holds its shape. Fold egg whites a third at a time into the chocolate mixture; mixing just enough to evenly combine.
Pour the batter into prepared pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 1 hour to 1 hour and 5 minutes. Cool in the pans for 10 minutes before removing to cool completely on a wire rack. Sift confectioners' sugar over the top of the cake before serving.
