Preheat oven to 350°F (175°C). Grease a 9×5-inch loaf pan with butter.
In a large bowl, whisk together flour, 1/2 cup sugar, baking powder, salt, and 1 teaspoon cinnamon.
In a medium bowl, whisk together milk, eggs, 1/4 cup melted butter, and vanilla extract until smooth.
Pour wet ingredients into the dry mixture. Gently fold until just combined—do not overmix.
Spread batter evenly into prepared loaf pan.
Mix remaining 1/2 cup sugar and 1 tablespoon cinnamon in a small bowl. Brush the top of the batter with the remaining 1/4 cup melted butter, then sprinkle cinnamon-sugar mixture generously over the top.
Bake for 25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Cool in pan for 10 minutes before slicing and serving warm.