Melt butter in a small saucepan over medium heat, stirring frequently, until golden brown. It will develop brown flecks and a nutty fragrance. (About 6-8 minutes.)

Pour the brown butter into a small bowl, and refrigerate until it's just firm, about 1 hour.

In a large mixing bowl, combine the brown butter and powdered sugar, beating until smooth.

Beat in the egg, egg yolk, and vanilla.

In a small bowl, combine flour and salt.

Gradually add the flour mixture to the mixing bowl, beating until blended. Dough should be a little bit sticky.

Using a cookie press, press dough 1-inch apart on parchment-paper lined baking sheets.

Sprinkle sugar or sprinkles over top of cookies, if desired.

Bake at 375 degrees for 6-8 minutes, or until set, but edges should not brown.

Remove to wire racks to cool completely.

Meanwhile, prepare caramel buttercream from the "Ginger Cookie Sandwiches with Caramel Buttercream" recipe.

Spread buttercream between two cookies.