Step 1: Make the Tart Crust

1. Preheat your oven to 375°F (190°C).
2. In a food processor, combine the flour, powdered sugar, and salt. Add the cold butter and pulse until the mixture resembles coarse crumbs.
3. Add the egg yolk and 2 tablespoons of cold water. Pulse until the dough comes together, adding another tablespoon of water if needed.
4. Roll the dough into a disc, wrap in plastic wrap, and refrigerate for 30 minutes.
5. Roll out the chilled dough on a floured surface to fit your tart pan. Press the dough into the pan and trim the edges. Prick the bottom with a fork.
6. Line the crust with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes, then remove the weights and bake for another 5-7 minutes until golden. Let cool completely.

Step 2: Make the Lemon Cream Filling
7. In a heatproof bowl, whisk together the eggs, sugar, lemon juice, and lemon zest. Place over a pot of simmering water (double boiler setup).
8. Cook, whisking constantly, until the mixture thickens and coats the back of a spoon, about 8-10 minutes.
9. Remove from heat and strain the mixture through a fine mesh strainer to remove zest and ensure a smooth texture.
10. Gradually whisk in the softened butter, one piece at a time, until fully incorporated. The mixture will become creamy and glossy.

Step 3: Assemble the Tart
11. Pour the lemon cream into the cooled tart crust and smooth the top with a spatula.
12. Refrigerate for at least 2 hours, or until the filling is set.

Step 4: Serve and Enjoy
13. Garnish with whipped cream, fresh berries, or a dusting of powdered sugar before serving. Slice and enjoy!