Preheat oven to 191 °C (190 °C). Brush phyllo sheets generously with melted butter, stacking them carefully. Cut the stacked phyllo into roughly 1-inch squares. Arrange the squares in a single layer on a baking sheet.

Bake for 10-15 minutes, or until golden brown and crispy. Let cool completely, then gently break into bite-sized pieces.

In a medium saucepan, whisk together milk, granulated sugar, cornstarch, flour, and egg yolks until smooth.

Cook over medium heat, stirring constantly, until the mixture thickens to a pudding-like consistency. Remove from heat and stir in vanilla extract.

Once the custard has cooled slightly (about 15 minutes), gently whisk in the heavy cream until fully incorporated.

In a small saucepan, combine mixed berries, lemon juice, and powdered sugar. Cook over medium heat until berries break down and the sauce thickens slightly. Strain if desired for a smoother coulis.

To assemble, layer a spoonful of the phyllo crisps at the bottom of serving glasses or bowls. Top with a generous layer of the vanilla custard, followed by a swirl of the berry coulis. Repeat layers.

Garnish with the remaining phyllo crisps and chopped pistachios before serving.