Cream the butter and sugar in a mixer using the paddle attachment. May also be done by hand with a woodern spoon or food processor. Add the yolks one at a time, mixing completely after the addition of each yolk. Sift the cornmeal, flour, and salt. Slowly add to the mixture on slow speed. When mixture just comes together, remove from mixer and turn out on a lightly floured surface. Knead until smooth and in a ball shape.
Cut ball of dough in half. Wrap one half of the dough in plastic wrap, press into a disc shape and refrigerate for at least 20 minutes to an hour.
Roll out other half of dough into an 11 inch circle, then transfer to a buttered 8 ½ inch tart pan with a removable bottom. Press in the dough making sure bottom and side edges are even. Sprinkle one teaspoon of polenta on bottom of shell to absorb any liquid from the peaches. Bake for 5-7 minutes. Brush bottom with glaze. Top with peach filling.
On a lightly floured surface roll out remaining half of dough so that it is large enough to cover tart shell. It is important that surface and rolling pin be floured ro avoid the dough from sticking, and thus breaking. Either fold the dough in half and place over tart shell, pressing and trimming edges, or cut-out shapes (such as hearts) and place on tart in a circular pattern, pressing at the edges.
Make an egg wash for the tart by lightly mixing 1 Tablespoon cream and 1 egg yolk in a small bowl. Lightly brush on tart crust and edges. Bake at 375 degrees until bubbly and golden brown, about 40-50 minutes. Serve warm or at room temperature.