Step 1: Prepare the Custard

1. Heat the Milk and Cream: In a medium saucepan, combine the milk and cream. Heat over medium heat until the mixture is warm but not boiling—just hot enough that it begins to steam and bubble around the edges.
2. Whisk the Egg Yolks: In a separate bowl, whisk together the egg yolks and sugar until smooth and pale. If you want a thicker custard, add a tablespoon of cornstarch to the eggs and sugar mixture at this stage.
3. Temper the Eggs: Gradually add a little of the warm milk and cream mixture to the egg yolks while whisking constantly. This is called “tempering” and helps to prevent the eggs from curdling. Once the egg mixture is warmed, slowly pour it back into the saucepan with the rest of the milk and cream.
4. Cook the Custard: Return the saucepan to the stove and cook over medium-low heat, stirring constantly with a wooden spoon or heatproof spatula. Continue to stir until the custard thickens and coats the back of the spoon (about 5-7 minutes). Don’t let it boil, as this can cause the custard to separate.
5. Finish the Custard: Once thickened, remove the custard from the heat and stir in the vanilla extract. Set aside to cool slightly, then place a piece of plastic wrap directly onto the surface of the custard to prevent a skin from forming. Let it cool completely before using.

Step 2: Assemble the Trifle

1. Prepare the Cake Layer: If you’re using a sponge cake, cut it into 1-inch cubes. If using trifle sponge fingers, simply dip each finger in the sherry (or fruit juice) briefly before layering them at the bottom of your trifle dish. Arrange a layer of soaked sponge at the bottom of your trifle bowl or glass dish.
2. Add the Fruit: Layer the soaked sponge with a generous amount of fresh mixed berries. You can use a combination of strawberries, raspberries, blueberries, or any seasonal fruits you like. If you prefer, you can also layer the fruit between the sponge layers for a more even distribution.
3. Add the Custard: Spoon the cooled custard over the fruit layer, spreading it evenly to cover the sponge and fruit completely. If the custard is too thick, you can whisk in a little milk to loosen it up before pouring it onto the trifle.
4. Whip the Cream: In a chilled mixing bowl, whip the heavy cream or double cream with the powdered sugar until stiff peaks form. The whipped cream should be thick and smooth, but not over-beaten.
5. Top with Cream: Spread a thick layer of the whipped cream over the custard, smoothing it out with a spatula. This is the final layer of the trifle.

Step 3: Garnish and Chill

1. Garnish the Trifle: Decorate the top of the trifle with a handful of fresh berries, a sprig of mint leaves, or toasted almonds for an extra touch of flavor and color.
2. Chill the Trifle: Cover the trifle with plastic wrap or a lid and place it in the refrigerator for at least 4 hours (preferably overnight) to allow the flavors to meld together and the layers to set.