Grating a bit of the pastry onto the top of the tart before baking will add a nice crunch.
In the bowl of a food processor, combine flour, sugar, cornmeal, and salt. Pulse to combine. Add butter, tossing with a wooden spoon to coat the butter cubes in flour, then pulse several times until the mixture resembles coarse oatmeal. Add egg yolk and 2 tablespoons milk, cream, or water, then pulse until the dough begins to come together in a ball. Add the additional tablespoon of liquid if it’s needed to bring the dough together. Transfer the dough to a lightly floured work surface and knead it briefly, then shape it into a disk about 5 inches across. Wrap in plastic and refrigerate at least 1 hour or overnight.
Using a lightly floured rolling pin, roll the dough into a shape about ½ inch wider than the tart pan you are using. Transfer the dough to the pan (loosely fold the dough in half so it doesn’t sag) and line the pan with it, being careful not to stretch the dough. Trim any excess dough from the rim of the pan, leaving a blunt, neat edge. Gather the trimmings into a ball (it should be about the size of a table tennis ball).
Wrap the tart and the small ball of dough in plastic and refrigerate 1 hour or up to 2 days.
Preheat the oven to 375°. Remove the tart pan from the refrigerator and spread marmalade evenly over the crust. Grate the chilled ball of pastry onto the marmalade, then sprinkle almonds over the top. Bake on a rack in the center of the oven until the pastry is golden, the filling is bubbly, and the almonds are toasted, about 40 to 50 minutes. Transfer to a wire rack to cool. When the tart is completely cool, dust with confectioners’ sugar. Serve at room temperature.