Prepare the Custard: Begin by gently heating 500ml of double cream in a saucepan. In a bowl, whisk together 5 egg yolks, 30g sugar, cornflour, and vanilla extract. Once the cream is warm, gradually pour it into the egg mixture, stirring continuously. Return the mix to the saucepan and heat gently, stirring until it thickens. Do not boil. Once thickened, set aside to cool.
Soak the Sponges: Layout 6 trifle sponges and sprinkle them evenly with 175ml of Madeira or dry sherry. Allow them to absorb the liquor.
Assemble the Filling: Spread 2 ½ tablespoons of raspberry jam over the soaked sponges. Arrange a layer of sponges at the bottom of a large trifle bowl. Scatter half of the 325g raspberries and sliced bananas over the sponges. Pour half of the cooled custard over the fruit layer. Repeat the layers once more, finishing with a layer of custard.
Prepare the Topping: Whip 325ml of double cream until it forms soft peaks. Spread this evenly over the top custard layer. Sprinkle 60g of toasted flaked almonds as a garnish.
Chill: Refrigerate the trifle for at least 2 hours before serving. This allows the flavors to develop fully.