In a small bowl, whisk together the flour, cornmeal, baking powder, and salt. In a stand mixer with the paddle attachment or in a food processor, mix the butter and granulated sugar together until smooth. Add the egg, egg yolk (keep the egg white from the second egg on hand for later) and almond extract and beat until combined. Gradually add the flour mixture and mix until the dough just comes together.

Transfer about one-third of the dough to a lightly floured counter and shape it into a log about 2 inches (5 cm) in diameter. Wrap it in plastic wrap and refrigerate it until needed.

Transfer the remaining dough to a buttered 9-inch (23-cm) tart pan with a removable bottom or a 9-inch (23-cm) springform pan. Using your hands, press the dough evenly into the bottom. If using a tart pan, press the dough up the sides to the rim of the pan and set the tart pan on a baking sheet. If using a springform pan, press the dough about 3/4-inch (2-cm) up the sides of the pan. Refrigerate the dough-lined pan until firm, at least one hour.

Preheat the oven to 375°F (190°C). Spread the jam or marmalade evenly over the dough in the pan. Cut the chilled dough into very thin discs with a sharp paring knife. Arrange them slightly overlapped in concentric circles over the jam to form a top crust.

Whisk the remaining egg white with a teaspoon of water until frothy; brush evenly over the tart lid and then sprinkle with coarse sugar. Bake until the top crust is golden brown, about 25 minutes. Let cool completely. This tart keeps beautifully for up to 3 days if well-wrapped at room temperature.