Beat 1 cup softened butter at medium speed with an electric mixer until creamy; gradually add 2 cups sifted powdered sugar, beating until well blended. Add 2 eggs and 1 egg yolk, beating until blended.
Combine flour and baking powder. Add to butter mixture, beating at low speed until blended. Shape dough into a ball, and wrap in plastic wrap. Chill 1 hour.
Roll dough to an 1/8-inch thickness on a lightly floured surface; cut with a 3-inch round cutter. Place on lightly greased, parchment paper-lined baking sheets; brush with lightly beaten egg white.
Stir together granulated sugar and ground cinnamon, and sprinkle evenly over cookies. Gently press 5 almond slices in a spoke design around center of each cookie.
Bake at 350° for 4 minutes; remove pan from oven, and gently press almonds into cookies again. Bake 4 more minutes or until edges are lightly browned. Remove cookies to wire racks to cool.