1. Preheat the oven to 350°F and grease or line a 9×5-inch loaf pan.

2. In a medium bowl, whisk together the flour, baking powder, and salt.

3. In a large bowl, beat the butter and granulated sugar until light and fluffy.

4. Add the eggs one at a time, then mix in the sour cream, lemon zest, lemon juice, and vanilla extract.

5. Stir the dry ingredients into the wet ingredients just until combined.

6. In a separate bowl, beat the cream cheese with 1/3 cup powdered sugar until smooth.

7. Spread half of the batter into the loaf pan, spoon the cream cheese mixture down the center, then cover with the remaining batter.

8. Bake for 50 to 60 minutes, or until a tester inserted into the bread portion comes out mostly clean.

9. Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely.

10. Whisk together 1/2 cup powdered sugar, 1 tablespoon lemon juice, and 1 to 2 teaspoons milk, then drizzle the glaze over the cooled loaf.