Adjust rack to lower third of oven and preheat to 350 degrees F. Cream the butter, sugars, and vanilla. Mix cornmeal, flour, and salt, and combine these with butter mixture. Shape this dough into 1-inch balls. Bake on a parchment-lined cookie sheet for 12 to 15 minutes. Dust with sifted powdered sugar while still warm, then a second time when cool.