In a large bowl, combine flour, salt, and sugar. Cut in the butter until crumbly. Add the egg yolk, sour cream, and vanilla. Mix just until dough comes together. Don’t overmix.
Wrap in plastic and refrigerate for at least 1 hour (or overnight).
2. Prepare Walnut Filling:
In a small saucepan, heat milk and sugar until sugar dissolves. Stir in ground walnuts, vanilla, and any optional flavoring. Let it cool.
3. Assemble the Cookies:
Preheat oven to 350°F (175°C).
Roll out dough on a lightly floured surface into a rectangle about ⅛ inch thick.
Cut into squares or rectangles (around 2.5 to 3 inches).
Place a small spoonful of walnut filling in the center, fold over or roll up like a mini log, and pinch to seal the ends.
Place seam-side down on a baking sheet lined with parchment.
4. Bake:
Brush with beaten egg. Bake for 20–25 minutes or until golden brown.
Let cool and optionally dust with powdered sugar.
📝 Tip:
You can also add raisins to the walnut filling or swap for poppy seed if you’re feeling adventurous!
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