Preheat oven to 350. Grease cookie sheets. In a medium bowl, cream the butter and sugar until light. Beat in the almond and vanilla extracts and the egg yolks. Next, stir in the chopped almonds, salt and flour. Roll the dough into 1 inch balls, dip the balls into the egg whites. Place cookies 2 inches apart on the prepared cookie sheet. Press a whole almond into the top of the ball, flattening the cookie a little bit. Bake for 8 to 10 minutes, until edges start to brown.