Preheat oven to 350°F (175°C). Line a 9x5-inch loaf pan with parchment paper, leaving overhang for easy removal.
For the cream cheese swirl, beat together cream cheese, ¼ cup sugar, 1 egg, 1 tablespoon flour, and 1 tablespoon lemon zest until smooth. Set aside.
In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
In a large bowl, cream butter and 1 cup sugar until light and fluffy, about 2-3 minutes.
Add eggs one at a time, beating well after each addition, then mix in 2 tablespoons lemon zest, 2 tablespoons lemon juice, and vanilla.
Fold in the flour mixture alternately with the sour cream, beginning and ending with flour (5 additions total).
Pour half the batter into the prepared pan, then spoon half the cream cheese mixture on top. Use a knife to swirl gently.
Repeat with remaining batter and cream cheese mixture, ending with a final swirl.
Bake for 50-60 minutes until a toothpick inserted in the center comes out clean or with a few moist crumbs. Tent with foil if needed to prevent over-browning.
Cool in the pan for 15 minutes, then use the parchment overhang to lift the loaf out to a wire rack to cool completely.
Once cooled, whisk together powdered sugar and 2-3 tablespoons lemon juice to make the glaze, then drizzle over the top of the bread.