Lightly spray an 8½x4½-inch loaf pan with cooking spray. Line pan with parchment paper, letting excess extend over long sides of pan.

In the bowl of a stand mixer, whisk together 1¼ cups (300 grams) warm water, 2 large eggs (100 grams), and melted butter by hand until combined.

In a medium bowl, whisk together flour, sugar, salt, yeast, and baking powder. Add flour mixture to egg mixture; using the paddle attachment, beat at low speed until combined. Scrape sides of bowl. Beat at medium speed for 5 minutes. (Batter will look very thick and hold its shape when you scrape the sides of the bowl.) Spoon batter into prepared pan, spreading into an even layer.

In a small bowl, whisk together 1 tablespoon (15 grams) water and remaining 1 egg (50 grams). Brush top of loaf with egg wash. Loosely cover with plastic wrap, and let rise in a warm, draft-free place (75°F/24°C) until doubled in size and risen just above sides of pan, 1 to 1½ hours.

Preheat oven to 400°F (200°C).

Brush top of loaf again with egg wash.

Bake for 15 minutes. Reduce oven temperature to 350°F (180°C), and bake until loaf is golden brown and an instant-read thermometer inserted in center registers at least 210°F (99°C), 30 to 35 minutes more. Let cool in pan for 5 minutes. Carefully run a knife along sides of loaf to loosen from pan. Using excess parchment as handles, remove from pan, and let cool completely on a wire rack. Store in an airtight container for up to 3 days, or wrap tightly in plastic wrap and freeze for up to 3 months.