Preheat the oven to 350 degrees Fahrenheit.

Grease two loaf pans (9.3” x 5.2” x 2.7”) well.

In the bowl of an electric mixer, cream together sugar, eggs, melted butter and vanilla extract. Add buttermilk and mix.

In a separate bowl, stir together flour, baking powder, salt and cream of tartar.

Add the flour mixture to the wet mixture and mix until incorporated, scraping down the sides in between.

In a small bowl stir together 1/3 c. granulated sugar and cinnamon.

Spread 1/4 of the batter into one prepared loaf pan and 1/4 into the other. Sprinkle 1/4 of the cinnamon/sugar mixture on top of the batter in one loaf pan and 1/4 of the mixture on top of the batter in the other loaf pan. Divide the remaining batter between the two loaf pans and spread evenly. Sprinkle the remaining cinnamon sugar mixture over the top of the batter on the two loaf pans.

Place loaf pans in the oven and bake for approximately 28 minutes, or just until a toothpick inserted into the center comes out mostly clean (moist crumbs are good). Let the loaves cool in the pans for 20 minutes, then carefully run a butter knife around the edges of the pan to help release. Carefully insert a metal spatula underneath the loaf all the way around to help release the bottom portion. Turn pan upside down with one of your hands underneath to catch the loaf. Let cool completely on a cooling rack, then slice and serve. Store in foil. Enjoy!