Heat milk in a saucepan until hot.

Whisk eggs, egg yolks, and sugar in a heatproof bowl.

Whisk in flour, cornstarch, and vanilla until smooth.

Gradually whisk in the hot milk.

Pour mixture into saucepan and cook over moderate heat, whisking constantly, until the custard thickens.

Strain the custard into a bowl and refrigerate until chilled, stirring occasionally.

Beat heavy cream with an electric mixer until stiff peaks form.

Beat in confectioners' sugar until combined.

Fold the custard into the whipped cream.

Cover with plastic wrap and refrigerate.

Preheat oven to 350°F.

Line baking sheets with parchment paper.

Lay one sheet of phyllo dough on a work surface and brush with melted butter.

Top with another sheet and brush with butter; repeat twice more.

Cut out nine 4-inch squares from the layered phyllo.

Cut each square diagonally to form 18 triangles.

Transfer triangles to baking sheets and cover with parchment paper.

Top with another baking sheet and bake until browned.

Repeat with the remaining phyllo sheets and butter.

Place a phyllo triangle on each of 8 plates.

Spread with dulce de leche and custard cream.

Top with another phyllo triangle; repeat 4 more times.

Finish with a sixth phyllo triangle.

Garnish each napoleon with a sliced strawberry.

Dust with confectioners' sugar and serve.