Cook 1/3 cup flour and 1 cup water in a small saucepan over medium heat, whisking constantly, until a thick paste forms, about 5 minutes. Add cream, honey and cook, whisking until honey dissolves.
Transfer mixture to a stand mixer fitted with a dough hook and add milk powder, yeast, kosher salt, 2 eggs, and 5 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.
Coat a large bowl with nonstick spray and transfer dough to bowl, turning 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 out dough onto a floured surface and divide into 6 pieces. 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 top of muffin pan), about 1 hour.
Preheat oven to 375 °F (190 °C). Beat the remaining egg with 1 tsp. water. Brush top of dough with egg wash and sprinkle with sea salt. Bake, rotating pan halfway through, until bread is deep golden brown, about 25–35 minutes. Let milk bread cool slightly in pan before turning out.