Make the Pound CakePreheat the oven to 325°F (165°C). Butter and line a 9x5-inch (23 x 12½ cm) loaf pan. Set aside.In a small bowl, whisk the flour, baking soda and salt together. Set aside.In the bowl of a stand mixer fitted with paddle attachment, cream the butter and sugar together for 5 minutes on high speed, until very light and fluffy.Add the whole egg, yolk and vanilla and beat for another 3 minutes, scraping down the sides of the bowl once or twice.Turn the mixer speed to low, then add ⅓ of the flour mixture, followed by ½ of the buttermilk. Continue alternating adding the flour and buttermilk, scraping down the bowl after each addition, until you have a smooth batter. Spread into the prepared pan and bake for about 40 to 45 minutes, until a skewer inserted in the center comes out clean.Leaving the cake in the pan, prick holes all over while still warm and drizzle the sherry evenly over the surface. Let cool completely.Cut the cake into small cubes, cover and refrigerate until needed. You can do this step the day before you build your dessert. (It also can be made, soaked and frozen for up to 8 weeks.)

Make the Ice Cream BasePlace a sieve over a medium, heatproof bowl and set aside near the stove.In another medium heatproof bowl, whisk the egg yolks, sugar and salt until smooth. Set aside.Warm the milk in a medium saucepan over low heat until it comes to a simmer, about 5 minutes.Temper the eggs by whisking constantly as you slowly pour in the hot milk, one ladleful at a time.Return the mixture to the pot and gently cook, stirring constantly for 6 to 8 minutes, until a thick custard is formed. Remove from the heat and immediately strain the mixture through the sieve to stop the cooking. Stir in the vanilla extract, then set aside to cool down fully before moving on to the next step (you can put the custard in the fridge or you can place the bowl over a bowl of ice water to cool quickly). This custard base can be made up to 24 hours in advance if needed.Whip the heavy cream in the bowl of a stand mixer fitted with a whisk attachment on medium-high speed until thickened, about 3 minutes. Gently fold the whipped cream into the chilled custard until evenly mixed. Refrigerate until needed.

Macerate the BerriesIn a medium bowl, combine the berries and sugar together and let sit at room temperature for 30 minutes, until the sugar is dissolved and the berries have released their juice. (I used blueberries, raspberries and strawberries that I quartered)

Assemble the TrifleButter a 9x5-inch (23x12½ cm) loaf pan. Line it with 4 large layers of plastic wrap to cover all the sides and hang about 3 inches (7½ cm) over the edges. Set asideGently fold the macerated berries into the ice cream base.Spread ⅓ of the ice cream into the prepared loaf pan.Add ½ of the soaked pound cake on top, pressing down into the ice cream, then spread on ½ the raspberry jam.Layer on ⅓ more ice cream, the followed by the remaining pound cake and jam. Push the trifle down into the pan to make sure there are no air bubbles. Top with the remaining ice cream to cover the pound cake.Cover the trifle with the overhanging plastic wrap and freeze for at least 6 hours, but preferably overnight.To serve, allow it to sit out at room temperature for 15 minutes before turning it out and unwrapping the trifle. Place on a serving plate and cut into 1-inch (2 ½ cm) thick slices. Store in the freezer for up to 8 weeks.