Preheat oven to 350°F (175°C). Line a 9x5” loaf pan with parchment.
Mix dry ingredients in a bowl: flour, baking powder, baking soda, salt.
Cream butter and sugar until fluffy. Beat in eggs, vanilla, lemon zest, and juice.
Combine dry ingredients alternately with milk until just mixed.
Make the swirl: Beat cream cheese, sugar, egg, and vanilla until smooth.
Layer batter and swirl: Half of the batter, cream cheese mix, then the rest of the batter. Swirl with a knife.
Bake for 50–60 min. Cool in pan 10 min, then transfer to a wire rack.