To make the Minted Custard Cream, put the milk and mint sprigs into a medium saucepan. Bring just to a simmer over a medium heat. Remove from heat and stand for 30 minutes to infuse. Remove the mint sprigs. Use a balloon whisk to whisk the egg yolks and sugar together in a heatproof bowl. Gradually whisk in the milk mixture until smooth and well combined. Return to the heat and stir constantly with the whisk over medium heat until the mixture thickens enough to coat the back of a spoon (do not simmer). Remove from the heat and stir in the vanilla. Pass the custard through a sieve into a heatproof bowl. Cover the surface with plastic wrap and refrigerate for 2 hours or until chilled.
To make the Brownie Cake, preheat oven to 160°C (140°C fan-forced). Grease a 20cm springform tin with melted butter and line the base with piece of non-stick baking paper. Place the chocolate and butter in a medium heatproof bowl over a saucepan of simmering water (don’t let the base of the bowl touch the water). Stir occasionally until chocolate and butter melt and the mixture is smooth. Remove bowl from saucepan and set aside to cool slightly. Use an electric mixer with a whisk attachment to whisk the sugar eggs and vanilla until thick and pale and a ribbon trail forms when the whisk is lifted. Whisk in the melted chocolate mixture. Sift together the flour and baking powder, add to the egg mixture and use a large metal spoon or spatula to fold in until just combined.
Pour mixture into the prepared tin and spread evenly. Bake for 40-45 minutes or until moist crumbs cling to a skewer inserted in the centre. Remove from the oven and cool in tin on a wire rack (this will take about 2 hours). Use a large serrated knife to cut the cake in half horizontally and then break it into chunks.
To make the Sweetened Raspberries, combine the frozen raspberries, sugar and lemon juice in a medium saucepan. Cover and cook over medium heat, stirring occasionally until the raspberries have just thawed. Remove from heat and set aside to cool.
To finish the Minted Custard Cream, fold the whipped cream through the chilled custard.
To assemble, layer the Custard Cream, Brownie Cake chunks, and Sweetened Raspberries and their juice in individual glasses.
The Brownie Cake will keep in an airtight continer at room temperature for up to 4 days. The Minted Custard Cream and Sweetned Raspberries will keep in separate airtight containers in the fridge for up to 2 days.
You can also layer this trifle on one large serving dish and serve in scoops.