How to Make the Cookie Dough:

Cup of Yum
1. !Prep: Preheat Oven to 350˚F. Line a 3/4 baking sheet with parchment (or 2 regular half sheets)
2. In the bowl of a stand mixer fitted with paddle attachment, add: 16 Tbsp butter, 3 egg yolks, 1/2 cup sour cream and mix medium/low speed just until combined. It won't be smooth.
3. Add 2 cups flour and add the last 1/2 cup slowly just until dough is no longer sticking to clean fingertips. When dough is ready, turn it out onto floured work surface then wash and dry your mixing bowl and make your meringue:

How to Make Meringue Cookie Filling:

1. In the bowl of your stand mixer, beat 3 room temperature egg whites on high speed 1 minute until thick and foamy. With the mixer on, slowly and gradually add 3/4 cup sugar. Once sugar is all in, continue beating on high for 5 min or until the meringue forms stiff peaks.

How to Assemble Meringue Shell Cookies:

1. While meringue is mixing, divide cookie dough into 4 pieces and roll each into a log. Cut each log into 15 equal pieces and roll them into balls between your hands. Roll each ball with a rolling pin into a 2" diameter circle.
2. Dollop a teaspoon of meringue into the center of each round then fold the cookie n half and in half again and lay it on it's side on the lined baking sheet. Space cookies at least 1/2" apart.
3. Stuff 3 walnut pieces into the meringue of each cookie then bake at 350˚F for 25 to 30 minutes or until edges are golden brown. Transfer to wire rack to cool to room temp before dusting with powdered sugar.