To decorate this, grate or shave a bit of white chocolate. Just after the cake has been glazed (before the ganache sets up), sprinkle it on top. This should be stored in the fridge; it does freeze, but it seems to lose flavor in the process. While this is really too much cake for two people, I think it would be charming as a Valentine's Day dessert or gift. Nice for a birthday cake in a small household, too.

Cake:

Adjust one rack to center of oven and one to bottom position in oven. Preheat oven to 350 degrees F. Have ready an 8" square pan that is 2" deep, and enough simmering water to fill it almost completely. Place butter pats into medium bowl; place egg into small cup and measure out sour cream. Allow these ingredients to stand at room temperature. Place 1/3 cup water in small pot with tight-fitting lid; set aside.

Grease two 6" round or heat-shaped layer pans with vegetable shortening. Line bottoms with wax paper cut to fit. Grease the paper, then dust the insides lightly with flour, knocking out any excess. Set aside.

In small bowl over simmering water on low heat (water should not touch bottom of bowl), melt chocolate, stirring often just until smooth. Remove from heat and hot water. Set aside to cool slightly. Into separate small bowl, sift together cake flour, baking powder, baking soda, and salt.

With large spoon or hand-held electric mixer, cream butter (which should be soft by now--if not, put in a warm place briefly until softened but not melted), sugar, and vanilla until well-mixed and fluffy. Beat in egg thoroughly. Add chocolate, which should still be slightly warm, and stir in. Stir in half the sifted dry ingredients, all of the sour cream, then the remaining dry ingredients, mixing after each just until combined (batter will be thick).

Place the 1/3 cup water in the covered saucepan on the heat until it comes to a boil. Meanwhile, place the 8" square pan on the bottom rack of the oven, and fill it almost to the top with the already-simmering water. Carefully push the rack back in and close the oven door. (Baking the cakes with steam helps them end up as slightly more even layers than they otherwise would.)

When the 1/3 cup of water is boiling, immediately pour about half of it into the cake batter and mix in (with a mixer, use lowest speed; by hand, you'll need a sturdy whisk). Scrape the bowl with a rubber spatula. Add remaining water and mix in just until combined. Batter will be thin. Divide evenly among prepared pans, then tilt pans slightly to run batter a bit higher up the sides. Place pans in preheated oven at least 2" apart.

Bake 18 to 23 minutes, turning back-to-front and exchanging positions of pans in oven about halfway through baking time. Cakes will still rise higher in center than on edges--OK. Layers are done when a toothpick inserted in center emerges with a few moist crumbs clinging to it. Do not overbake. Remove to cooling rack. Cool layers only 5 minutes, then loosen edges from pan and invert onto cooling rack. Remove pan; gently peel off wax paper. Re-invert to cool right side up. Cool completely before glazing.

For Ganache Glaze: In small heatproof bowl, combine chopped chocolate and salt. In small saucepan over low heat, heat cream until very hot, stirring occasionally. Pour about 2/3 of hot cream over chocolate; let stand about 2 minutes. Gently whisk until smooth. (If necessary, place bowl of chocolate over simmering water on low heat--water should not touch bottom of bowl--and whisk often just until smooth. Remove from heat and hot water.) Gradually whisk remaining hot cream into chocolate mixture. Let stand until ganache has cooled to room temperature, gently whisking occasionally.

Meanwhile, with large, serrated knife, trim tops of completely cooled cake layers so the layers are level. Invert one layer upside down onto serving plate so that bottom of cake faces up. Shortly before ganache is ready, drizzle half of optional liqueur onto cake surface.

When ganache has cooled to room temperature, whisk to mix. Spread a generous amount onto liqueur-drizzled cake surface, then place second trimmed layer, right side up, on top. Drizzle with remaining optional liqueur. Pour ganache slowly onto middle of top layer; smooth down sides of cake, then make an even layer on top. If desired, decorate top sparingly with shaved white chocolate. Chill, covering tightly when cold. If possible, remove from refrigerator about 30 minutes before serving. Store in refrigerator.

2 to 4 servings