In a bowl, combine all purpose flour, rye flour, and kosher salt. Whisk well and set aside.
2 cups all purpose flour, 1 ½ cups + 2 tablespoons dark rye flour, 1.5 teaspoons kosher salt
*Extra step if using instant yeast! Add warm milk (110-115°F), molasses, and yeast to a mixing bowl. Whisk and let it sit for about 10 minutes.
2 ¼ teaspoons instant yeast, ¾ cup whole milk, 3 tablespoons molasses
After 10 minutes, the mixture should be foamy. Then, you can add melted and cooled butter, along with the egg and egg yolks.
6 tablespoons unsalted butter, 1 large large egg, 2 large egg yolks
Add about ⅓ of the flour mixture, and then whisk it well until it's completely incorporated. Add the rest of the dry ingredients to the wet ingredients. With a dough hook in a stand mixer, knead on low speed for 8-10 minutes until the dough is smooth, elastic, and pulls away from the sides of the bowl.
Grease a clean bowl with some oil, then transfer the dough to the bowl and cover with a clean kitchen towel or plastic wrap. Place it in a warm place to allow it to rise.
Allow the dough to rise until it's about twice it's size. This should take about 1 - 1 ½ hours. When touched, the dough should not spring back right away and it should instead leave an imprint where your finger was.
Now, shape the buns into 12 roughly equal-sized pieces. You can use a food scale to weigh them out if you'd like. There's no need to flour your work surface, this dough is pliable and not sticky. On the underside of each piece of dough (working with one piece at a time) create a round ball shape, and pinch the dough where it comes together near the back.
Place the dough ball with the pinched side down onto a work surface. Use your palm to lightly roll the dough ball into a round shape, applying gentle pressure, and roll until the bread forms a tight dough ball.
Place the rolls, seam-side down into your greased baking sheet. Cover, and let rise again for about 45 minutes to an hour. While the dough is rising for the second time, preheat the oven to 375°F.
The rolls are done rising when they are touching, soft, and uffy. Again, if you tough one with your finger, an indent should remain and the dough should not spring back on you.
If the seams come untucked during the second rise, simply re-pinch them and place them flat side down in the baking pan again.
Whisk together milk and an egg white and brush the tops of the buns. This will give them a glossy finish.
1 large egg white, 1 tablespoon whole milk
Now, just bake the buns at 375°F for 20-25 until the buns are golden brown. When they come out of the oven, you can rub them with butter for an even yummier finish.