Preheat the oven to 350 degrees F. Grease a 9×5-inch loaf pan and set aside.
In a large bowl, add sugar, eggs, sour cream, lemon zest, lemon juice, vanilla, and oil. Mix until smooth.
Slowly add the baking powder, salt, and flour to the wet ingredients until fully combined.
For the cream cheese swirl: mix together the cream cheese and powdered sugar until smooth.
Add half of the lemon batter to the loaf pan then spoon about half the cream cheese mixture on top. Swirl together using a butter knife.
Top with the rest of the lemon batter and spoon the remaining cream cheese mixture, then swirl together to create a marbled look.
Bake uncovered for 45 minutes, then cover with foil and bake for another 15-25 minutes until a toothpick inserted into the center comes out clean.minutes,
Cool completely before slicing.