Steps
1. Prepare the walnut sweet shortcrust dough by mixing flour, powdered sugar, ground walnuts, and salt.
2. Rub in the cold butter until mixture resembles breadcrumbs.
3. Add the egg yolk and mix to form a dough. Chill for 30 minutes.
4. Roll out dough to fit a small tart mold (about 8cm diameter), place it inside, and chill again for 15 minutes.
5. Preheat oven to 180°C (350°F). Blind bake the tart shell with parchment and weights for 12 minutes, remove weights and bake 5 more minutes until golden. Cool.
6. For pastry cream, heat milk to just below boiling.
7. Whisk egg yolk, sugar, and cornstarch until smooth.
8. Temper egg mixture by slowly adding hot milk, then return to low heat, stir until thickened.
9. Add vanilla extract, cool completely.
10. Whip heavy cream with powdered sugar and coffee powder until soft peaks form to make coffee chantilly.
11. Fill the cooled tart shell with pastry cream.
12. Pipe or spoon coffee chantilly over the custard layer.
13. Heat pitahaya puree with sugar syrup briefly and brush over the chantilly to create a shiny glaze.
14. Garnish with fresh mint leaves and crushed walnuts.
15. Dust lightly with powdered sugar.
16. Weigh the final tart and adjust portions to 80 grams if needed.
17. Serve chilled.