In a large bowl, beat butter and oil with a mixer at medium speed until smooth. Add sugar and lemon zest, and beat at medium-high speed until fluffy. Add eggs, one at a time, beating well after each addition.
In a medium bowl, whisk together flour and baking powder. Gradually add flour mixture to butter mixture, beating until mixture is smooth. Cover and refrigerate dough for at least 1 hour.
Preheat oven to 350˚. Line baking sheets with parchment paper.
Roll dough into approximately 36 (5x.25-inch) ropes. Fold each rope in half lengthwise, and twist ends together. Place 1 inch apart on prepared pans.
In a small bowl, whisk together egg yolks and 1 tablespoon water. Brush mixture over cookies, and sprinkle with sesame seeds.
Bake until edges of cookies are golden brown, about 12 minutes. Let cool on pans for 2 minutes. Remove from pans, and let cool completely on wire racks.
Recipe by Victoria at https://victoriamag.com/greek-lemon-butter-cookies-recipe/