Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan or line it with parchment paper for easy removal.

In a large mixing bowl, whisk together the granulated sugar, eggs, sour cream, oil, lemon zest, lemon juice, and vanilla extract. The mixture should be smooth and well combined.

In another bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, stirring gently just until no dry spots remain. Be careful not to overmix.

In a small bowl, beat the softened cream cheese and powdered sugar until smooth and creamy. You want the consistency to be thick but spreadable.

Pour half of the lemon batter into the prepared loaf pan. Spoon the cream cheese mixture in a line down the center. Use a knife or skewer to gently swirl it through the batter. Pour the remaining lemon batter over the top, spreading it out evenly.

Tip: Swirl just enough to create a ribbon without blending the layers completely.

Bake for 50 to 60 minutes, or until a toothpick inserted into the center comes out clean. The top should be golden and the center fully set.

Tip: Tent the loaf with foil after 40 minutes if the top is browning too quickly.

Allow the loaf to cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely. Slice and serve as is, or dust with powdered sugar for an extra touch.