Instructions

1. To make the trifle, Preheat oven to 350 F (180 C). Grease and line bottom and sides of two 8-in (20 cm) square baking pans with parchment paper.
2. In a heatproof bowl set over a saucepan of simmering water, melt butter and unsweetened chocolate, stirring constantly. Make sure water does not touch bottom of bowl. Once melted, remove from heat and whisk in 2 cups (500 ml) sugar and ¼ tsp (1 ml) salt. Stir until sugar is fully dissolved and mixture is slightly cooled.
3. In a separate bowl, lightly whisk together 4 eggs and 1 tbsp (15 ml) vanilla. Add to chocolate mixture and whisk until fully incorporated.
4. In another bowl, lightly whisk flour and cocoa together and fold into chocolate mixture. Do not over beat. Stir in chocolate chips and walnuts, if using.
5. Divide batter evenly between prepared baking pans and bake for 30 to 35 minutes, or until skewer inserted in centre of brownies comes out clean. Remove from oven and invert onto a wire rack to cool completely. Once cool, cut brownies into 2-in (5 cm) squares and store in an airtight container until ready to use. Brownies can be made up to 3 days ahead and stored in refrigerator in an airtight container.
6. In a large heatproof bowl, whisk together egg yolks, ½ cup (125 ml) sugar and remaining ¼ tsp (1 ml) salt, until thick, pale yellow and increased in volume.
7. Warm ¼ cup (60 ml) whipping cream in a small saucepan over low heat, or microwave for 15 to 20 seconds on high, and stir in instant coffee powder until dissolved. Add to egg yolk mixture.
8. Set bowl with egg yolk mixture over a saucepan with simmering water, making sure water does not touch bottom of bowl. Whisk constantly, until egg mixture thickens further and reaches 160 F (71 C). Remove from heat and continue stirring to cool slightly. Add mascarpone and mix until smooth. Add Kahlua and rum, if using, and mix well. Set aside.
9. In a medium bowl, whisk 1 cup (250 ml) whipping cream until peaks formed hold their shape. Lightly mix ⅓ of whipped cream into mascarpone mixture until no white streaks remain. Fold in rest of whipped cream until blended. Set aside.
10. In another medium bowl, whisk together remaining 1½ cups (375 ml) whipping cream, remaining 2 tbsp (30 ml) sugar, remaining 1 tsp (5 ml) vanilla extract and cream of tartar until peaks formed hold their shape
11. Line bottom of large trifle bowl with brownies. Spread ⅓ of mascarpone mixture evenly over brownies. Spread ½ of whipped cream evenly over mascarpone layer. Repeat layering with brownies, ⅓ of mascarpone mixture and remaining whipped cream. Add one more layer of brownies and top with remaining mascarpone mixture. Chill for at least 4 hours before serving. Can be made up to 1 day in advance; if making ahead, loosely cover and store in refrigerator.
12. To make the chocolate bowl decoration, inflate balloon and knot the end. Place balloon in a cup, knotted end down, to hold it upright. Brush surface with oil.
13. In a heatproof bowl set over a saucepan of simmering water, melt ⅔ cup (150 ml) chocolate, making sure water does not touch bottom of bowl. Remove from heat, add ⅓ cup (75 ml) chocolate and stir continuously until all the chocolate is melted and there are no lumps remaining.
14. Slowly pour melted chocolate over greased balloon and allow chocolate to set for about 1 hour. Place in refrigerator if ambient temperate is warm or humid and chocolate is still soft to touch.
15. When ready to use, cut a small hole near the knotted end of the balloon and control release of air very slowly. Gently remove deflated balloon and use chocolate bowl to garnish trifle. Can be made up to 2 days in advance and stored, uncovered, in a cool, dry place.
16. To serve, decorate with Chocolate Bowl Decoration, if using, and/or chocolate curls, truffles and bonbons of your choice.