Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper.
In a large bowl, whisk together the flour, sugar, baking powder, and salt.
In another bowl, mix the milk, yogurt, egg, oil, and vanilla until smooth.
Pour the wet mixture into the dry and stir just until combined. Don’t overmix—nobody likes tough bread.
Pour half the batter into the loaf pan. Mix the cinnamon and sugar together in a small bowl and sprinkle half over the batter.
Add the rest of the batter, then top with the remaining cinnamon sugar. Use a knife to swirl it around a bit—it doesn’t need to be perfect.
Bake for 50–55 minutes or until a toothpick comes out clean. Let cool for 15 minutes before slicing (if you can wait that long).