These cookies get their name from their piped windowpane design.
Heat oven to 375 degrees. Whisk together flour, salt, and cornmeal. In the bowl of an electric mixer fitted with the paddle attachment, beat butter and sugar on medium speed until light and fluffy. Add eggs one at a time, beating after each addition. Reduce speed to low, and add flour mixture. Combine thoroughly.
Line an 11-by-17-inch baking pan with parchment. Press half the dough evenly into the bottom of pan. Place another piece of parchment over dough; rub the bottom of a spoon over parchment to get dough completely smooth; remove parchment. Using an offset spatula, spread jam on dough in an even layer.
Fit a pastry bag with a #11 plain tip. Fill pastry bag with remaining dough. Pipe parallel lines of dough spaced 1/2 inch apart over jam. Pipe perpendicular lines spaced 1/2 inch apart over first lines. Bake until golden, about 30 minutes. Transfer to a wire rack to cool. Cut into about 48 1 1/2-by-3-inch bars, or about 24 3-inch squares.
