Preheat the oven to 375 and grease a loaf pan with nonstick cooking spray. Set aside.
In a bowl, combine Jiffy corn muffin mix and sugars. Mix well.
Add sour cream, egg, milk, melted butter, and vanilla extract and mix until smooth. Do not overmix the batter.
Add coarse sea salt to the bottom of the prepared loaf pan.
Pour cornbread batter into the pan and bake for 27-32 minutes or until browned and the center, when a toothpick is inserted comes out clean. This time varies depending on the oven, so just check.
Cool the cornbread in the pan before removing and slicing to serve. It could crumble apart if you attempt to remove it while very hot.