In the bowl of a stand mixer fitted with the paddle attachment, beat ¾ cup (95 grams) flour, hot milk, and yeast at low speed until well combined. Cover bowl with plastic wrap, and let stand in a warm, draft-free place (75°F/24°C) until mixture is bubbly, 25 to 30 minutes.
Add sugar, butter, eggs, salt, orange blossom water, and remaining 3 cups (381 grams) flour to yeast mixture. Beat at low speed until well combined, stopping to scrape paddle and bottom and sides of bowl.
Switch to the dough hook attachment, and beat at low speed until dough is smooth and elastic, 20 to 25 minutes.
Spray a large bowl with cooking spray. Place dough in bowl, turning to grease top. Cover and let rise in a warm, draft-free place (75°F/24°C) until doubled in size, 1½ to 2 hours.
Line a baking sheet with parchment paper.
Turn out dough onto prepared pan, and gently pat into a 6-inch circle. Using your elbow or hands, make an indentation in center of dough. Stretch indentation to create a 3½-inch hole in center of dough, folding outside edges of dough circle under as needed to maintain round shape. Loosely cover with a lightly greased piece of plastic wrap, and let rise in a warm, draft-free place (75°F/24°C) until very puffed up, 45 minutes to 1 hour.
Preheat oven to 350°F (180°C).
Brush egg yolk all over dough. Using a sharp knife or lame, score dough to create a pound sign/hashtag pattern.
Bake until golden brown and an instant-read thermometer inserted near center registers 190°F (88°C), about 20 minutes, covering with foil during final 7 minutes of baking to prevent excess browning. Let cool on pan for 10 minutes. Remove from pan, and let cool on a wire rack for 30 minutes. Best served warm. Store in an airtight container for up to 3 days.