1. Using an electric mixer fitted with the paddle attachment, beat butter and sugar until creamy and smooth, about 2 minutes. Add vanilla and zest. Beat well, scraping sides of bowl as necessary. With mixer on low speed, mix in flour, 2 tablespoons cornmeal, and salt until well combined, about 3 minutes. Form dough into two logs about 1 1/2 inches in diameter; wrap in plastic wrap, and chill at least 1 hour.

2. Preheat oven to 300 degrees. Place remaining 1/4 cup cornmeal on a sheet of parchment or waxed paper. Remove plastic from chilled dough; roll logs in cornmeal to coat. Slice into 1/4-inch rounds. Place on a baking sheet about 1 inch apart. Bake until pale golden all over, 25 to 30 minutes. Cool on a wire rack. Dust with sugar.