Combine flours, butter, sugar, and yeast in the bowl of a heavy-duty stand mixer fitted with a dough hook attachment. Beat on low until very well combined, about 1 minute. Add milk, egg yolks, and 1/4 cup of the water. Increase speed to high, and beat 3 minutes. Add kosher salt; beat until dough starts to come together, 1 minute. Turn dough out onto a lightly floured work surface, and knead until a supple, shiny dough forms, about 3 minutes. Shape dough into a ball, and place in a large bowl coated with cooking spray, turning to grease dough. Cover bowl with plastic wrap, and let rise in a warm place (80°F to 85°F), free from drafts, until doubled in bulk, about 1 1/2 hours.
Divide dough into 16 equal (2-ounce) portions. Roll each into a ball. Place in a 9-inch metal baking pan coated with cooking spray. Cover with plastic wrap, and let rise in a warm place (80°F to 85°F), free from drafts, until very puffy, about 1 hour.
Preheat oven to 325°F.
Whisk together egg and remaining 1 tablespoon water. Remove plastic wrap from rolls, and brush tops of rolls with egg mixture; sprinkle with pretzel salt. Bake in preheated oven until golden brown and a thermometer inserted into center of rolls registers 190°F, 30 to 35 minutes. Cool in pan on a wire rack 10 minutes. Remove from pan, and serve immediately.