For the dough:
• ½ cup (1 stick) unsalted butter, plus more to butter bowl and pans, as needed
• 1 cup milk
• 5 tablespoons granulated sugar
• 1 tablespoon active dry yeast
• 1½ teaspoons kosher salt
• 1 large egg plus 1 large yolk
• 3 to 3½ cups all-purpose flour, as needed
• 1 egg yolk (for basting)
• 1 1/2 pounds slab bacon(uncooked)
• 1 medium onion
To make the dough, melt the ½ cup butter in a small saucepan over medium-low heat. Add the milk and granulated sugar and heat just to lukewarm (about 100°F), stirring to dissolve the sugar.
Pour the warm milk mixture into a bowl. Stir in the yeast. Allow the mixture to sit for 10 minutes. Stir in the salt. Beat the whole egg and yolk together and add to the yeast mixture. Stir in the flour I cup at a time until you have a sticky dough.
Scrape the dough out onto a floured work surface and knead, about 5 minutes, adding a little more flour as necessary, until you have a nice smooth dough. Butter a large bowl. Place the dough in the prepared bowl and cover with plastic wrap. Put the bowl in a warm place and allow the dough to rise for 2 hours until tripled in volume.
Dice bacon, onion into very small pieces; the more uniform the better.
Cook in pan with 1/2 cup of water Season with a little black pepper. When the dough has risen, punch down and start forming buns. Take walnut size lump of dough and stretch to 3-inch diameter Put 1 1/2 teaspoons filling in center. Fold in half and seal edges like a turnover.Mix one egg yolk with 2 Tbsp water and brush the top of each roll.