Heat your oven to 350 degrees F. Grease a 9x5 inch loaf pan with butter or nonstick spray, then press a strip of parchment paper into the bottom and up the two long sides so the baked loaf lifts out easily.

In a large bowl, whisk together the flour, 3/4 cup brown sugar, 2 teaspoons cinnamon, baking powder, baking soda, and salt until the mixture looks evenly blended and there are no brown sugar clumps remaining.

In a separate smaller bowl or large measuring cup, whisk the eggs, milk, sour cream, melted butter, and vanilla together until smooth. The mixture should look uniform with no streaks of egg.

Pour the wet ingredients into the dry ingredients and fold with a rubber spatula just until no dry flour streaks remain. The batter will be thick. Stop stirring as soon as it comes together because overmixing leads to a dense, tunnel-filled loaf.

Scrape the batter into the prepared pan and smooth the top with the spatula. In a small bowl, stir together the 2 tablespoons of brown sugar and 1/4 teaspoon cinnamon, then sprinkle the mixture evenly over the top of the batter.

Bake on the center rack for 50 to 58 minutes. The loaf is done when the top is deep golden brown, the bread has pulled slightly away from the sides of the pan, and a toothpick inserted into the center comes out with just a few moist crumbs. If the top is browning too fast after 35 minutes, lay a loose sheet of foil over it.

Set the pan on a wire rack and let the bread cool in the pan for 15 minutes before lifting it out using the parchment handles. Let it cool for at least another 20 minutes before slicing so the crumb has time to set. Slicing too early will give you a gummy interior.