Step 1: Preheat your oven to 350°F (175°C) and grease and flour a 9×5-inch loaf pan, or line with parchment paper for easy removal.
Step 2: In a large bowl, whisk together the all-purpose flour, baking powder, salt, and 1/2 cup granulated sugar. Make a well in the center.
Step 3: In a separate medium bowl, whisk together the egg, milk, 1/4 cup melted butter, and vanilla extract until well combined.
Step 4: Pour the wet ingredients into the well of the dry ingredients. Mix with a spatula until just combined. Be careful not to overmix; a few lumps are okay.
Step 5: Pour the batter into the prepared loaf pan and spread evenly. Bake for 50-60 minutes, or until a wooden skewer inserted into the center comes out clean. If the top browns too quickly, tent loosely with foil.
Step 6: While the bread bakes, prepare the cinnamon sugar topping. In a small bowl, combine the 1/2 cup granulated sugar and 1 tablespoon ground cinnamon. Set aside. Melt the remaining 1/4 cup butter in a separate small bowl.
Step 7: Once the bread is baked, remove it from the oven and immediately invert it onto a wire rack. While still warm, brush all sides generously with the melted butter. Then, sprinkle and roll the bread in the cinnamon sugar mixture, ensuring an even coating on all sides.
Step 8: Let the cozy cinnamon sugar donut bread cool completely on the wire rack before slicing and serving. This allows the cinnamon sugar coating to set and the flavors to fully develop.