Steps
1. Preheat the oven to 180°C (350°F).
2. In a bowl, cream together the softened butter and powdered sugar. Add the egg yolk and mix well.
3. Gradually incorporate the flour and ground pistachios to form a dough.
4. Press the dough into a small tartlet mold, ensuring an even layer on the bottom and sides.
5. Bake the crust for about 10 minutes or until lightly golden. Let it cool.
6. In a saucepan, combine the milk, egg, granulated sugar, vanilla bean paste, and cornstarch. Whisk until smooth.
7. Cook over medium heat, stirring constantly, until the mixture thickens. Remove from heat and let cool slightly.
8. Pour the custard into the cooled tartlet shell and refrigerate for at least 30 minutes until set.
9. Before serving, sprinkle the top with crushed pistachios.