This square cake is dark and moist, with a fudge-all-the-way-through texture. What else would you expect from 1 pound (455 g) of chocolate? The cake can be spread with a ganache glaze for even more chocolate richness.

Ingredients
Cake
Mixing time 10 minutes

• 13 oz (370 g) semisweet (plain) chocolate, chopped
• 3 oz (85 g) unsweetened chocolate, chopped
• 3/4 c up (170 g) unsalted butter, cut into pieces
• 1 tsp instant coffee granules dissolved in
• 1 tbsp water
• 4 large eggs
• 1 1/2 cups (300 g) granulated sugar
• 1/2 tsp salt
• 1 tsp vanilla extract (essence)
• 1 cup (130 g) unbleached all-purpose (plain) flour
• 1 cup (240 ml) ganache (recipe below), cooled until thickened but pourable (optional)
• Powdered (icing) sugar for dusting (optional)
• 1 qt (960 ml) vanilla ice cream or flavour of your choice

Ganache
Mixing and cooking time 5 minutes

• 1 c up (240 ml) heavy (double) cream
• 1 tbsp unsalted butter
• 9 oz (255 g) bittersweet chocolate, chopped, or
• 1 1/2 cups (255 g) bittersweet chocolate chips
• 1 tsp vanilla extract (essence)

Directions
Cake

1 Position a rack in the middle of the oven. Preheat the oven to 350°F (180°C/gas mark 4). Butter a 9-in (23-cm) square pan with sides 2 in (5 cm) high. Line the bottom with a piece of parchment (baking) paper long enough to extend over opposite sides of the pan. Butter the paper.

2 Put both chocolates, the butter, and dissolved coffee in a heatproof bowl (or the top of a double boiler) and place it over, but not touching, barely simmering water in a saucepan (or the bottom of the double boiler). Stir until the chocolates and butter are melted and smooth. Remove from over the water and set aside to cool slightly.

3 In a large bowl, using an electric mixer on medium speed, beat the eggs, sugar, salt, and vanilla until fluffy and lightened in colour, about 1 minute. Stop the mixer and scrape the sides of the bowl as needed. On low speed, mix in the melted chocolate mixture until blended. Mix in the flour just until no white streaks remain. Spread the batter evenly in the prepared pan.

4 Bake until the top of the cake is shiny and firm and a toothpick inserted in the center comes out with moist crumbs clinging to it, about 35 minutes. Cool the cake in the pan on a wire rack for 1 hour.

5 If using the ganache, pour it over the cake, tilting the pan to spread it evenly. Cool the cake in the pan thoroughly. The cake will become firm. If omitting the glaze, dust the cooled cake with powdered sugar, if desired. Use the overhanging ends of parchment (baking) paper to lift the cake from the pan.

6 Serve the cake at room temperature with scoops of ice cream. The cake can be covered and stored at room temperature for up to 3 days.

Ganache and whipped ganache
1 In a medium saucepan, heat the cream and butter over low heat until the cream is hot and the butter melts. The hot cream mixture should form tiny bubbles and measure about 175°F (80°C) on an instant-read thermometer; do not let the mixture boil as a skin might form on the top. If this happens, use a spoon to lift off the skin and discard it.

2 Remove the pan from the heat, add the chocolate, and let stand in the hot cream mixture for about 30 seconds to soften. Whisk the ganache just until all of the chocolate is melted and the ganache is smooth. Stir in the vanilla.

3 If the ganache will be poured or spread, let it cool and thicken slightly, about 30 minutes. It can be covered and refrigerated for up to 1 week; if it becomes too firm, it can be warmed over low heat, stirring to soften it evenly.

4 To make whipped ganache, cover the warm ganache and let stand at room temperature until firm, 3 to 4 hours, depending on the quantity and the temperature of your kitchen. Or, cover and refrigerate the ganache until the edges are firm and the center is slightly thickened, 1 to 2 hours. You can speed up the process to 30 minutes or less by pouring the ganache into a 9-by-13-in (23-by-33-cm) or larger baking dish. Drop a teaspoon of the cold ganache on a plate; set aside to compare the colour with that of the beaten ganache.

5 Place the cold ganache in a bowl and whisk until it changes from a dark chocolate colour to a medium chocolate colour and thickens slightly, about 30 seconds. Compare with the ganache on the plate. The whipped mixture should look lighter in colour—similar to a dark, good-quality milk chocolate. Use immediately.

6 When whipping ganache, let it cool and thicken to a firm but not hard texture. Refrigerating it will firm it more quickly, but it should chill for only 1 or 2 hours until the edges are firm.

7 Use a whisk to beat the mixture for about 30 seconds until the color lightens from a dark brown to a medium brown. The taste and texture will change from fudgelike to creamlike. Using a whisk prevents the ganache from being whipped too vigorously, which could turn it grainy. Whipped ganache should be spread immediately, as it firms up quickly and becomes difficult to spread smoothly.

Choices: Other flavourings for ganache include almond extract; ground cinnamon; dissolved instant coffee granules, finely grated orange or lemon zest; fruit purees; and rum, brandy, or other liqueurs. Start with a small quantity, taste the mixture, and keep adding to your taste. Begin with 1 tbsp for the liquor or liqueurs and 1 tsp for instant coffee or grated zest.  Quantities can always be increased.

Makes 9 to 12 servings of cake and 2 cups (480 ml) of ganache .

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Excerpted from Chocolate Cakes by Elinor Klivans. Copyright 2010 by Chronicle Books. Excerpted with permission by Chronicle Books. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.