Preheat the oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan.

In a medium bowl, whisk together flour, sugar, baking soda, baking powder, salt, and cinnamon until well combined.

In a large bowl, combine milk and lemon juice. Allow it to stand for 5 minutes. Whisk in oil, vanilla, and eggs until combined.

Gradually add dry mixture to wet ingredients in three parts, stirring gently after each addition.

In a small bowl, mix together brown sugar, cinnamon, and melted butter until smooth.

Pour half of the batter into the prepared loaf pan and create three parallel lines of cinnamon mixture over the batter.

Gently swirl the cinnamon mixture into the batter with a skewer or knife.

Add remaining batter and repeat the layering and swirling process.

Bake for about 50 minutes, or until a toothpick inserted in the center comes out clean.

Cool in the pan for 5-10 minutes before inverting onto a wire rack.