**Prepare the Crust:** In a large bowl, whisk together the flour and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining. Gradually add ice water, one tablespoon at a time, mixing until the dough just comes together. Form into a disc, wrap in plastic, and refrigerate for at least 30 minutes.

Preheat oven to 375°F (190°C). On a lightly floured surface, roll out the chilled dough into a 12-inch circle. Carefully transfer the dough to a 9-inch tart pan with a removable bottom. Trim excess dough and crimp the edges as desired. Prick the bottom with a fork several times. Bake for 10-12 minutes, or until lightly golden. Remove from oven and reduce oven temperature to 350°F (175°C).

**Prepare the Rhubarb Filling:** In a medium bowl, combine the chopped rhubarb, 1/2 cup granulated sugar, 2 tablespoons flour, and 1/2 teaspoon vanilla extract. Toss gently to coat the rhubarb. Pour the rhubarb mixture evenly into the pre-baked tart crust.

**Prepare the Custard Topping:** In a separate medium bowl, whisk together the eggs, 1/2 cup granulated sugar, heavy cream, milk, 1/2 teaspoon vanilla extract, and optional pinch of nutmeg until well combined and smooth.

Carefully pour the custard mixture over the rhubarb in the tart pan. Bake for 35-40 minutes, or until the custard is set and the top is lightly golden. A knife inserted into the center of the custard should come out clean. If the crust edges appear to be browning too quickly, you can cover them loosely with aluminum foil.

Allow the tart to cool completely on a wire rack before serving. This will help the custard set fully. Serve at room temperature or chilled, perhaps with a dollop of whipped cream or a scoop of vanilla ice cream.