In a mixing bowl, combine all-purpose flour and salt, then cut in very cold unsalted butter using a pastry cutter or fork until the mixture resembles coarse crumbs. Gradually add ice water, mixing until the dough just forms. Shape it into a disc, wrap in plastic, and refrigerate for at least 30 minutes.

Preheat your oven to 375°F (190°C). Roll the chilled pastry into a 12-inch circle, about 1/8 inch thick, and transfer to a tart pan, pressing into the edges. Chill the crust for 15 minutes before blind baking for 15-20 minutes until golden around the edges. Remove and set aside.

Chop fresh rhubarb into small pieces and place in a bowl. Sprinkle granulated sugar over the rhubarb to macerate for 15-20 minutes. Drain any excess liquid to prevent a soggy tart.

In a large mixing bowl, whisk together eggs, egg yolk, granulated sugar, all-purpose flour, and a pinch of salt until smooth. Heat heavy cream over medium until just simmering. Gradually temper the cream into the egg mixture, whisking continuously until fully combined.

Return the mixture to the saucepan and cook over medium heat, stirring gently until it thickens slightly and coats the back of a spoon.

Layer the prepared rhubarb evenly in the pre-baked crust, pour the creamy custard mixture over it, and bake at 350°F (175°C) for 30-35 minutes until the edges are set and the center jiggles slightly.

Remove the tart from the oven and cool at room temperature for 2-3 hours to allow the custard to set.