Preheat your oven to 350 degrees Fahrenheit or 175 degrees Celsius. Grease a 9 by 5-inch loaf pan with butter or nonstick spray. You can also line it with parchment paper, leaving a little overhang for easy lifting.

In a medium bowl, whisk together the all-purpose flour, baking powder, salt, and ground cinnamon. Set this aside.

In a large bowl, beat the softened butter and granulated sugar together until light and fluffy. This usually takes 2 to 3 minutes with a hand mixer. Scrape down the sides of the bowl as needed.

Add the eggs one at a time, beating well after each addition. Then mix in the vanilla extract. The mixture should look smooth and slightly pale.

Add the dry ingredients to the butter mixture in three additions, alternating with the milk. Start and end with the dry ingredients. Mix just until the flour disappears. Overmixing can make the loaf dense, so stop as soon as the batter looks combined.

Transfer the batter to the prepared loaf pan and smooth the top with a spatula. Bake for 50 to 60 minutes. The loaf is done when a toothpick inserted into the center comes out clean or with just a few moist crumbs.

Let the loaf cool in the pan for about 10 minutes. Run a thin knife around the edges, then carefully turn the loaf out onto a wire rack.

While the loaf is still warm, brush the entire surface with the melted butter. Mix the sugar and cinnamon for the topping in a small bowl, then sprinkle it generously over the top and sides. Press lightly if needed, but avoid rubbing. Let the loaf cool completely so the topping can set.