Preheat oven to 350 degrees F and grease a standard loaf pan.
In a large bowl, add sugar, eggs, sour cream, lemon zest, juice, vanilla, and oil. Mix until smooth and well combined.
In another bowl, sift together flour, baking powder, and salt.
Slowly add the dry ingredients to the wet until fully combined, then set aside.
For the cream cheese swirl: In a small bowl, mix together the cream cheese and powdered sugar until smooth.
Add half of the batter to the prepared pan and spoon about half the cream cheese mixture on top, then swirl together with a knife.
Top with the rest of the batter and spoon the remaining cream cheese mixture. Carefully swirl together to create a marbled look.
Bake bread for 65-70 minutes, covering with foil for the last 20-30 minutes to prevent the top from browning.
Allow the bread to fully cool before slicing to allow the cream cheese to set.
