1. In a bowl, with a mixer on high speed, beat butter and granulated sugar until fluffy. Add hard-cooked egg yolks, uncooked egg yolk, uncooked whole egg, and salt; beat on medium speed until blended. Stir in flour, then beat until well blended.
2. Shape dough into 1-inch balls; cover with plastic wrap. On a lightly floured board, roll each ball under your palm into a 6-inch-long rope. On a 12- by 15-inch baking sheet (you'll need 3 total), twist each rope into a figure eight and press ends lightly together; space twists about 1 inch apart. Beat remaining egg white to blend; lightly brush over twists. Sprinkle with pearl sugar.
3. Bake in a 350º oven until twists are golden brown, about 20 minutes (16 to 18 minutes in a 325° convection oven). If using 1 oven, switch pan positions after 10 minutes. With a wide spatula, transfer twists to racks to cool. Serve warm or cool.