Add all-purpose flour, baking powder, and kosher salt to medium mixing bowl. Whisk to combine. Set aside.
Add sugar, butter, and lemon zest to bowl of stand mixer. Beat on medium with paddle attachment until pale and smooth, about 3 minutes. Scrape down the bowl with a spatula, if necessary.
Add eggs 1 at a time to sugar mixture. Beat on low just until combined.
Add 1/2 the flour mixture to the sugar mixture. Beat on low just until combined.
Add the sour cream and lemon juice. Beat on low just until combined. Scrape down the bowl with a spatula, if necessary.
Add the remaining flour mixture to the sugar mixture. Beat on low until well combined, about 30 seconds.
Transfer batter into prepared loaf pan. Smooth top with offset spatula.
Bake in preheated oven for 60 minutes, or until a toothpick inserted in the center comes out clean.
Remove pan from oven and place on wire rack. Cool 15 minutes and then remove loaf from pan. Cool completely.