Preheat the oven to 350°F (175°C) and grease a loaf pan.

Whisk together the flour, baking powder, cinnamon, and salt in a bowl.

Cream the butter and sugar together until fluffy. Add the eggs one at a time, blending well after each addition, then mix in the sour cream.

Combine the dry ingredients with the wet ingredients gradually until just mixed.

Pour half the batter into the pan, sprinkle with half the cinnamon-sugar mixture, then add the remaining batter. Top with more cinnamon-sugar.

Bake for 50-60 minutes until golden brown and a toothpick inserted in the center comes out clean.

Allow to cool before serving.