Steps
1. Preheat your oven to 200°C (400°F).
2. In a bowl, cream together the softened butter and powdered sugar until light and fluffy.
3. Add the egg yolk and mix well.
4. Gradually add the flour and salt, mixing until a dough forms.
5. Roll out the dough and cut into circles to fit into a muffin tin. Press the dough into the bottom and sides of each cup.
6. In another bowl, whisk together the egg, milk, sugar, and vanilla extract until smooth.
7. Pour the custard mixture into each pastry shell, filling them about 3/4 full.
8. Bake in the preheated oven for 15-20 minutes, or until the custard is set and the tart edges are golden.
9. Remove from the oven and let cool slightly before serving.