Prepare the pastry cream. In a medium saucepan, bring the milk, sugar, and salt to a simmer. Stir until the sugar is completely dissolved. Remove from heat.
In a large bowl, whisk together the cornstarch, egg, and egg yolks. Whisk a little of the hot milk mixture into the egg mixture to temper the eggs. Slowly add the remainder of the milk and whisk until incorporated.
Transfer this mixture back into the saucepan used to heat the milk. Bring the mixture to a boil. Stir constantly with a whisk to prevent lumps. Cook until the mixture thickens. Remove from heat and strain through a fine strainer into a bowl. Add butter and vanilla and mix until well incorporated. Cover the cream with plastic wrap, making sure it touches the cream so it doesn’t develop a skin. Refrigerate until completely cool.
Combine the strawberries with the sugar and allow the strawberries to macerate and release juices.
Prepare the whipped cream. In a large bowl, beat the cream, sugar, and vanilla. Whip until stiff peaks form. Reserve in the refrigerator.
Assemble the trifle. Place a layer of pound cake at the bottom of a trifle bowl. Top with a layer of strawberries. Add some of the juices released by the strawberries. Sprinkle pistachios on top. Add a layer of pastry cream and then a layer of whipped cream. Repeat the process of layering ending with whipped cream.
Decorate with quartered strawberries, whole strawberries, and pistachios. Drizzle some of the juices from the macerated strawberries on top. Serve.