How to Make It
Combine flour, sugar, salt, and yeast in the bowl of a stand mixer fitted with the paddle attachment. Whisk together milk, cream, and powdered milk in a medium bowl. Whisk in egg.
Add milk mixture to flour mixture. Beat on medium-low speed until combined, about 2 minutes.
Fit mixer with the dough hook attachment. Beat on medium speed until dough is smooth, about 10 minutes. (Pull up a section of dough, and stretch as thin as possible. If dough is see-through but does not rip, your dough is complete. If it rips, continue beating until dough can be stretched.)
Lightly grease a large bowl with cooking spray, and place dough in greased bowl, turning to coat. Cover with plastic wrap, and let rise until almost doubled in size, about 1 hour and 30 minutes.
Transfer dough to a work surface; cut into thirds. Flatten each piece, and tightly roll into tubes. Place tubes, seam sides down, on work surface; cover with lightly greased plastic wrap. Let rest 15 minutes.
Working with 1 dough piece at a time, roll into a 20- x 12-inch rectangle on a lightly floured surface. Brush with a scant 11/2 tablespoons melted butter; cut lengthwise into 4 strips, and cut strips crosswise into 6 strips each, making 24 rectangles. Stack all 24 dough rectangles. Repeat with remaining 2 dough pieces and remaining melted butter. Arrange stacks in a lightly greased tube pan, standing up like little books, allowing gaps between dough pieces.
Cover pan with lightly greased plastic wrap, and let stand in a warm place (80°F), free from drafts, until dough just reaches top edges of pan, about 1 hour. Preheat oven to 325°F.
Remove plastic wrap, and bake in preheated oven until bread is golden brown and puffed, 35 to 40 minutes. Transfer to a wire rack, and let stand in pan 5 minutes. Remove from pan, and place on a platter. Brush with melted butter, and sprinkle with flaky sea salt.