Preheat the oven to 350. Line baking sheets with parchment paper

In a large bowl, beat butter, sugar and vanilla on medium speed until creamy, add egg yolks one at a time, beating after each addition.

In a small bowl, combine flour and salt. Gradually add to butter mixture, beating until combined. Shape dough into 11/2 inche balls

In a medium bowl whisk egg whites until frothy. Place nuts in a shallow bowl or plate. Dip dough balls into egg white, letting the excess drip off, roll in nuts, place on parchment lined baking sheet, 2 inches apart. Using your thumb or the back of a small spoon, gently make an indentation in the center of the ball.This is where the caramel will go later.

Bake for 10 minutes, remove from oven and press down on middle of cookie one more time,I used the back of a 1/4 teaspoon here since they are hot, be gentle. Return to oven until lighty browned 2 to 4 more minutes. Cool on pan 2 minutes then transfer to rack to cool compleatly. Fill centers with warm caramel and let stand until firm. Store in a airtight container.

FOR CARAMEL FILLING

In a large skillet, not non stick, stir together sugar, water and corn syrup. Cook, stirring occasionally,over medium heat for8 to 10 minutes until just honey colored. Remove from heat and add butter, stirring until melted. Stir in cream and vanilla extract until combined and smooth.Let cool about 7 to 10 minutes before filling cookies.

To fill carefully, with a spoon drizzle center of cookie to fill with caramel, let stand to cool and set.

TIP WITH CARAMEL Do NOT overheat only cook it to a honey color or it will cool to a hard consistancy. Make caramel after cookies are cool so they are ready for the warm caramel. Be careful, caramel is very hot to work with. Also you probably will have some leftover caramel, its great on ice cream!