The Ultimate Moist Banana Bread

In a large mixing bowl, mash 1 ½ cups ripe bananas, i.e. about 3 large bananas[/adjustable] with a fork until broken up. You want to make sure you break up any large pieces or you will have large pieces of banana in your bread and it can cause it to bake weird.

Mix in melted ½ cup unsalted butter, ½ cup light brown sugar, and ½ cup granulated sugar, then stir until combined. 
NOTE: To achieve the dense and moist texture we’re going for you MUST mix by hand! Using an electric mixer will whip too much air into the bread and affect the texture.

Add in the 2 large eggs, ½ cup sour cream, and 2 teaspoons vanilla extract then stir until just combined. Once mixed, add in the 1 teaspoon baking soda, ½ teaspoon baking powder, and ½ teaspoon cinnamon then mix again.

Lastly, mix in ½ teaspoon salt, 1 tablespoon cornstarch, and 1 ½ cups all-purpose flour and stir until just combined. You do not want to mix this for any longer than it takes for the flour to disappear or it will become dense and chewy. Do not overmix!

Grease a 9" metal loaf pan ⅔ full (you can usually fill up heavy batters like this almost all the way, just being sure to leave about ½″ at the top without having it rise over). 
Note: Because there are varying size of “standard” loaf pans (some are wider than others and therefore fit more), you may end up with a little extra batter. You can scoop the rest into muffin tins and bake.

(Read this step carefully!) Bake at 350°F for 60 minutes on the bottom or middle rack of your oven. After 45 minutes of it baking, gently cover the top of your loaf with foil to prevent the top from browning. When baking, place your loaf near the bottom/middle of oven. You do not want it too close to the top or the top will brown faster than the inside can cook.

Test doneness by sliding a toothpick or skewer into the center while it's still in the oven. If it comes out clean (or just with a crumb or two) it's ready.
Once baked, you should ideally allow banana bread to cool in the pan for about an hour to allow it to set and cool. If not eating right away, cover with foil and let it completely cool before putting in a ziploc bag. Wrapping it in plastic too soon will trap the steam and could make your bread mushy. See notes below for storage instructions.