In mixer bowl, cream butter, sugar and brown sugar. Add peanut butter. Mix well. Mix in egg yolks and vanilla. Stir in chocolate. On low speed, add flour mixture until dough forms.
In shallow dish, whisk egg white until foamy. Place peanuts in another shallow dish.
Using a 1-inch cookie scoop, scoop dough and roll into 48 balls. Dip each in egg whites. Roll in peanuts and place on parchment lined baking sheets. Using your thumb, indent center of each cookie. Bake 8 minutes, remove from oven and gently re-dent each cookie. Bake 6 to 8 minutes longer or until set. Cool on pans 10 minutes. Remove to rack. Cool completely.
Salted Caramel Filling
In a small saucepan over medium heat, melt butter. Add brown sugar, cream and salt. Stir occasionally until mixture comes to a gentle boil. Allow to boil gently 5 minutes, stirring constantly.
Add vanilla, stir well and remove from heat to cool.
When cool and slightly thickened, fill center of each cookie.