*In a measuring cup add 1 tablespoon (15 grams) of white vinegar or lemon juice, add enough milk to make 1 cup (225 grams), let sit 10 minutes before using.
For room temperature remove from fridge 30-45 minutes before using.
Pre-heat oven to 350F (180C). Lightly grease and flour a 9 inch (22-23 cm) loaf pan.
In a small bowl mix together the cinnamon, brown sugar and butter, this will be used as the swirl.
In a large bowl beat together the sour milk, melted butter, eggs and vanilla for about 1 minute until combined. In a large bowl whisk together the flour, sugars, baking powder, baking soda, cinnamon and salt. Add the wet ingredients to the dry ingredients and mix just until combined. It will be a bit lumpy. Do not over mix as this will cause a tough heavy bread.
Spoon half the batter into the prepared loaf pan, top with half the cinnamon mixture and swirl with the tip of a knife, top with the remaining batter and remaining cinnamon mixture. Swirl again and bake for approximately 45-50 minutes or until the toothpick comes out clean. Let cool in the pan for approximately 15-20 minutes then move to a wire rack. Let cool completely before slicing and serving. Enjoy!