Preheat your oven to 375°F (190°C). In a large mixing bowl, combine all-purpose flour, finely ground almonds, and a pinch of salt. Cut in cold unsalted butter until the mixture resembles coarse crumbs. Gradually add ice-cold water until dough forms. Shape into a disk, wrap, and chill for 15 minutes.

Roll out the chilled dough on a floured surface until 1/8-inch thick. Fit into tart pan, trim excess. Prick base with a fork, line with parchment and fill with weights. Blind-bake for 10 minutes until lightly golden. Remove weights and cool.

In a bowl, whisk heavy cream, whole milk, eggs, sugar, vanilla, and a pinch of salt until smooth. Set aside.

In a skillet, combine chopped rhubarb, sugar, lemon juice, and cornstarch. Cook over medium heat for 5-7 minutes until rhubarb is tender. Remove from heat and cool slightly.

Pour custard over pre-baked crust, spreading evenly. Spoon tender rhubarb over custard. Bake for 20-25 minutes until custard is set with a slight jiggle.

Cool on a wire rack for 20 minutes. Dust with powdered sugar before serving at room temperature.