Combine flour, 1 cup sugar, baking powder, baking
soda, 1 1/2 tsp. cinnamon, salt, buttermilk, oil,
eggs, and vanilla in a large bowl. Beat 3 minutes.
Pour into prepared loaf pan. Smooth top.
Combine 2 Tbsps. white sugar, 1 tsp. cinnamon, and
butter, mixing until crumbly. Sprinkle topping over
smoothed batter. Using a knife, cut in a light
swirling motion to give a marbled effect.