Doris's Velvet Chocolate Cake

Preheat oven to 350 degrees. Lightly coat an 8-by-3-inch round cake pan with margarine, and line bottom with a round of parchment paper; set aside.

In a heat-proof bowl or the top of a double boiler set over a pan of simmering water, melt the chocolate with the margarine and instant espresso, stirring until smooth and glossy. Remove bowl from pan of water, and let mixture cool slightly. Whisk in egg yolks one at a time, beating well after each addition.

In the bowl of an electric mixer fitted with the whisk attachment, beat egg whites on high speed to soft peaks. With machine running, slowly add granulated sugar, beating until stiff glossy peaks form. Stir about 1/4 of the whites into chocolate base to lighten it. Gently but thoroughly fold in remaining whites until thoroughly combined.

Pour batter into prepared cake pan. Place in a roasting pan, and pour hot water into roasting pan to come halfway up sides of cake pan. Carefully transfer to oven, and bake until top of the cake is just set in the center, about 35 minutes. Transfer to a wire rack to cool completely, then transfer to refrigerator for at least 4 hours and up to overnight.

Run a paring knife around edges of cake to release from pan, and unmold (if the cake doesn't come out of pan, briefly dip bottom of cake pan in warm water; do not leave in water too long, or cake will melt). Invert cake onto serving platter, and dust top with confectioners' sugar. Serve in very thin slices.