In a large mixing bowl beat butter with an electric mixer on medium to high speed for 30 seconds. Add granulated sugar, baking powder, and salt. Beat until combined, scraping sides of bowl occasionally. Beat in egg yolks and vanilla bean paste until combined. Gradually beat in milk until combined. Beat in as much of the flour as you can with the mixer. Using a wooden spoon, stir in any remaining flour (dough will be sticky). Divide dough in half. Cover and chill for at least 2 hours or until dough is easy to handle.
Preheat oven to 350°F. Lightly grease a cookie sheet; set aside. Working with one portion of dough at a time, pinch off 1-inch pieces of dough. On a lightly floured surface, roll each piece into a 9-inch rope. Shape rope into a circle, crossing rope about 1 inch from the ends. Fold the ends back over circle. Moisten ends; press ends to circle to seal. Place cookies 2 inches apart on the prepared cookie sheet.
In a small bowl combine egg and the water. Brush cookies lightly with egg mixture; sprinkle with pearl sugar. Bake for 8 to 10 minutes or until cookies are firm and edges are lightly browned. Transfer to a wire rack; cool.
Layer cookies between sheets of waxed paper in an airtight container; cover. Store at room temperature for up to 3 days or freeze for up to 3 months.