Preheat the oven to 300 degrees . Line 2 large cookie sheets with silicone parchment paper.
Place the sugar in a medium bowl. Scrape the vanilla bean seeds into the sugar; stir well. Whisk in the flour and salt. Make a well in the center of the dry ingredients. Pour in the butter, egg whites and vanilla. Whisk until smooth and slightly runny (like pancake batter).
Transfer 6 generous teaspoonfuls of the batter to each cookie sheet, placing them about 5 inches apart and using your finger to scrape the batter off the spoon. Using the back of the measuring spoon, swirl each mound into a thin 4-inch cookie, making sure that each cookie is about the same thickness. Sprinkle each cookie with a generous pinch of almonds or other topping.
Working with one sheet at a time, bake the cookies until pale golden in the center and golden brown around the edges, about 15 minutes.
Working quickly and using a thin metal spatula, divide the warm cookies between 2 rolling pins or 1 rolling pin and a tall drinking glass. The cookies will curve as they cool. Let sit until crisp, about 3 minutes.