Cook 1/3 cup of flour and 1 cup of water in a small saucepan over medium heat, whisking constantly until a thick paste forms, about 5 minutes. Then, add the cream and honey, and continue cooking while whisking until the honey dissolves.
Transfer the mixture to a stand mixer fitted with a dough hook, and add the milk powder, yeast, kosher salt, 2 eggs, and 5 cups of flour. Knead on medium speed until the dough is smooth, about 5 minutes.
Add the butter, one piece at a time, fully incorporating it into the dough before adding the next piece, until the dough is smooth, shiny, and elastic, about 4 minutes.
Coat a large bowl with nonstick spray and transfer the dough to the bowl, turning it to coat. Cover with plastic wrap and let rise in a warm place until doubled in size, about 1 hour.
Lightly coat a 6-cup jumbo muffin pan with nonstick spray. Turn the dough out onto a floured surface and divide it into 6 pieces. Then, divide each piece into 3 smaller pieces. Place 3 pieces of dough side by side in each muffin cup. Let rise again in a warm place until doubled in size and puffing over the top of the muffin pan, about 1 hour.
Preheat the oven to 375°F (190°C). Beat the remaining egg with 1 teaspoon of water. Brush the top of the dough with the egg wash and sprinkle with sea salt. Bake, rotating the pan halfway through, until the bread is deep golden brown, about 25 to 35 minutes. Let the milk bread cool slightly in the pan before turning it out.