1. Preheat the oven to 350°F. Grease a 9×5-inch loaf pan and line it with parchment paper.

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

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

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

5. Add the dry ingredients to the wet ingredients and stir just until combined.

6. In a separate bowl, beat the cream cheese, powdered sugar, egg yolk, vanilla extract, and lemon zest until smooth.

7. Spread half of the lemon batter into the prepared pan.

8. Spoon the cream cheese filling down the center of the batter, leaving a little space around the edges.

9. Add the remaining lemon batter over the top and smooth gently. Swirl once or twice with a knife if desired.

10. Bake for 55 to 65 minutes, or until the bread portion is set and a toothpick comes out with moist crumbs.

11. Cool in the pan for 15 to 20 minutes, then transfer to a wire rack to cool completely.

12. Whisk powdered sugar, lemon juice, and milk or cream until smooth, then drizzle over the cooled loaf before slicing.