Preheat oven to 350°F (180°C). Grease and flour a 9-inch round or 8-inch square baking pan.
In a medium bowl, sift and mix flour, baking powder, baking soda, and salt.
In a separate large bowl, beat softened butter and sugar until light and fluffy. Add eggs one at a time, mixing well after each addition.
Stir in vanilla extract, lemon juice, and lemon zest.
Alternate adding flour mixture and milk to the wet ingredients, beginning and ending with flour, mixing just until combined.
Fold in sour cream until fully incorporated.
Pour batter into prepared pan and smooth surface.
Bake for 28–32 minutes, or until a toothpick inserted into the center comes out clean.
Cool completely before slicing and serving.