How to make a chocolate mousse cake

Ingredients

• 1/2 cup butter , softened1/2 1/2cup cup(125 mL) (125 mL) butter, softened
• 3/4 cup granulated sugar 3/4 3/4cup cup(175 mL) (175 mL) granulated sugar
• 2 eggs 2 2eggeggs
• 1 tsp vanilla 1 1tsp tsp(5 mL) (5 mL) vanilla
• 1-1/4 cups sifted cake and pastry flour 1-1/4 1-1/4cups cups(300 mL) (300 mL) sifted cake and pastry flour
• 1/4 cup cocoa powder 1/4 1/4cup cup(60 mL) (60 mL) cocoa powder
• 1 tsp baking powder 1 1tsp tsp(5 mL) (5 mL) baking powder
• 1/4 tsp baking soda 1/4 1/4tsp tsp(1 mL) (1 mL) baking soda
• 1/4 tsp salt 1/4 1/4tsp tsp(1 mL) (1 mL) salt
• 2/3 cup buttermilk 2/3 2/3cup cup(150 mL) (150 mL) buttermilk
• Chocolate Mousse:
• 1 pkg (7 g) gelatin 1 1pkg pkg(7 g) gelatin
• 2/3 cup milk 2/3 2/3cup cup(150 mL) (150 mL) milk
• 4 egg yolks 4 4egg yolkegg yolks
• 1/4 cup granulated sugar 1/4 1/4cup cup(60 mL) (60 mL) granulated sugar
• 1 Pinch salt 1 1Pinch Pinchsalt
• 4 oz bittersweet chocolate , melted4 4oz oz(113 g) (113 g) bittersweet chocolate, melted
• 2 oz milk chocolate , melted2 2oz oz(57 g) (57 g) milk chocolate, melted
• 2 tbsp dark rum , (optional)2 2tbsp tbsp(30 mL) (30 mL) dark rum, (optional)
• 1 tsp vanilla 1 1tsp tsp(5 mL) (5 mL) vanilla
• 2 cups whipping cream 2 2cups cups(500 mL) (500 mL) whipping cream
• Chocolate Gouache:
• 6 oz bittersweet chocolate , chopped6 6oz oz(170 g) (170 g) bittersweet chocolate, chopped
• 2/3 cup whipping cream 2/3 2/3cup cup(150 mL) (150 mL) whipping cream

Preparation

Grease 9-inch spring form pan; line bottom with parchment or waxed paper. Set aside.

In large bowl, beat butter with sugar until fluffy; beat in eggs, 1 at a time. Beat in vanilla. In separate bowl, sift together flour, cocoa, baking powder, baking soda and salt. Stir into butter mixture alternately with buttermilk, making 3 additions of dry ingredients and 2 of buttermilk. Scrape into prepared pan; smooth top.

Bake in centre of 350°F (180°C) oven until cake tester comes out clean, 30 minutes. Let cool on rack for 20 minutes. Remove side of pan; let cool. (Make-ahead: Cover and set aside for up to 24 hours.)

Chocolate Mousse: Meanwhile, in small bowl, sprinkle gelatin over 2 tbsp water; set aside. In small saucepan, heat milk over medium-high heat just until tiny bubbles form around edge. In heatproof bowl, whisk together egg yolks, sugar and salt; slowly whisk in milk. Place bowl over saucepan of simmering water; cook, stirring, until custard is 160°F (70°C) and thick enough to coat back of spoon, about 8 minutes. Remove from heat.

Stir in gelatin mixture until melted. Whisk in bittersweet and milk chocolates, rum (if using) and vanilla. Refrigerate, stirring twice, until cold and mixture can mound on spoon, about 15 minutes.

In separate bowl, whip cream; whisk one-quarter into chocolate mixture. Fold in remaining cream.

Line side of 10-inch spring form pan with parchment paper to extend 1 inch above rim. Cut cake horizontally in half. Place 1 layer in prepared pan. Pour in half of the mousse, letting mousse extend over side of cake. Top with remaining layer. Pour in remaining mousse to cover top and side of cake; smooth top. Refrigerate until set, 2 hours.

Chocolate Gouache: Place chocolate in bowl. In small saucepan, bring cream to boil; pour over chocolate and whisk until smooth. Let cool for 30 minutes. Pour over mousse; smooth with palette knife. Refrigerate until set, about 1 hour. (Make-ahead: Cover and refrigerate for up to 24 hours.)