Step 1

Place 2 tablespoons unsalted butter in a small bowl and let sit out at room temperature to soften while you prepare the dough.

Step 2

Place 1/4 cup plus 2 tablespoons water and 2 tablespoons of the bread flour in a small saucepan and whisk until smooth. Heat over low heat, stirring constantly with a rubber spatula, until the mixture becomes thick and paste-like, 1 to 2 minutes. Immediately scrape into a large bowl and let cool to room temperature.

Step 3

Place 1/2 cup whole milk in a small microwave-safe bowl or measuring cup. Microwave on high until warm but not hot (about 100°F), 20 to 30 seconds. Sprinkle 1 1/2 teaspoons active dry yeast over the milk, stir to dissolve, and set aside until small bubbles form around the edge of the bowl, 5 to 7 minutes. Meanwhile, whisk together the remaining 2 1/2 cups bread flour, 1 1/2 teaspoons kosher salt, and 2 tablespoons granulated sugar together in a medium bowl.

Step 4

Add the yeast mixture, 1/3 cup heavy cream, and 1 of the large eggs to the cooled flour paste and whisk until smooth. Add the flour mixture and stir with a wooden spoon until a shaggy dough forms.

Step 5

Transfer the dough onto a lightly floured work surface and knead until a rough ball of dough forms, 2 to 3 minutes. If the dough is too sticky, knead in 1 tablespoon flour at a time until it comes together. Add the softened butter and knead until the dough is completely smooth, 3 to 4 minutes, adding more flour if needed to prevent sticking.

Step 6

Coat a large bowl with butter, then transfer the dough into it. Cover with a kitchen towel or plastic wrap and let rise in a warm place until doubled in volume, 1 1/2 to 2 hours. Meanwhile, line a 8 1/2-inch loaf pan with parchment paper so that there is excess parchment hanging off the long sides, then coat the parchment and sides of the pan with butter.

Step 7

Punch down the dough and transfer it onto a work surface. Divide the dough into 4 pieces. Using a rolling pin, roll one piece of dough into a 8x5-inch rectangle. Fold a third of the dough lengthwise over toward the center, then do the same thing from the other side. Starting at a short end, roll the dough up into a tight coil. Repeat with the remaining dough pieces.

Step 8

Place the coils seam-side down in the loaf pan with the spirals against the long side of the pan. Let rise uncovered in a warm place until doubled in volume, 30 to 40 minutes. Meanwhile, arrange a rack in the middle of the oven and heat the oven to 350°F. Crack the remaining egg into a small bowl and whisk until no streaks remain.

Step 9

Brush the beaten egg onto the dough and sprinkle with flaky salt if desired. Bake until the top is golden-brown and shiny, 25 to 30 minutes. Let cool for at least 30 minutes before slicing.