Step 1

Combine ⅓ cup of the flour and the water in a small saucepan and place over medium heat, whisking constantly, until a thick paste forms (it should be a little looser than a roux), about 3 to 5 minutes. Reduce the heat to low, add the heavy cream and honey and whisk until honey dissolves. Remove from the heat.

Step 2

Transfer the mixture to the bowl of a stand mixer fitted with a dough hook and add the milk powder, yeast, kosher salt, eggs, and 5 remaining cups flour. Knead on medium speed until dough is smooth, about 5 minutes. Add butter, a piece at a time, fully incorporating into dough before adding the next piece, until dough is smooth, shiny, and elastic, about 4 minutes (the dough may look loose and separated at first, but it will come together, just keep kneading).

Step 3

Coat a large bowl with nonstick cooking spray and transfer dough to bowl, turning to coat. Cover with plastic wrap and let rise in a warm, draft-free place until doubled in size, about 1 hour.

Step 4

Coat two 9- by 5-inch loaf pans with nonstick cooking spray. Turn the dough out onto a floured surface and divide into 12 pieces. Nestle the pieces side-by-side to create 2 rows down length of each pan.
 Cover with a clean dish towel.

Step 5

Let the dough rise in a warm, draft-free place until doubled in size (dough should be just puffing over top of pan), about 1 hour.

Step 6

Preheat oven to 375 degrees F. In a small bowl, whisk together the egg and water for the egg wash. Brush top of the dough with egg wash. Sprinkle with flaky sea salt, if desired. Bake, rotating pans halfway through, until bread is deep golden brown and an instant-read thermometer inserted into the center registers 190 degrees F, about 30 minutes. Let the bread cool in the pans on a wire rack for 10 minutes before turning them out, then let cool completely before slicing.