Preheat oven at 350-degrees. Cut parchment paper to fit long-ways in a loaf pan, sticking up on either side as a sling. Apply nonstick spray into pan, place paper, then spray again. Set aside.
In a big bowl, stir together flour, baking powder, cream of tartar, 1 cup white sugar, and salt. Gradually mix in the milk, vanilla extract, oil, and egg, until just combined.
In a small bowl, combine the remaining 1/2 cup sugar with the cinnamon.
Spread about half the batter in the loaf pan. Sprinkle half the cinnamon-sugar on top, followed by about half the nuts (if using). Add rest of the batter. Use a knife to swirl batter, bringing the blade up and down a bit, to marble the layers together. Sprinkle rest of the cinnamon-sugar across the top followed by the nuts (if using). Swirl the batter again.
Bake for 55 to 65 minutes, until a toothpick stuck deep in the middle comes out clean. About halfway through the bake, add foil over the top to prevent overbrowning.
Let cool in pan for 10 minutes, then use parchment sling to lift loaf onto a rack to fully cool.
Well-wrapped loaf keeps at room temperature as long as 5 days. Slices can also be frozen for later enjoyment.