Preheat oven to 350 degrees F (175 degrees C). Grease an 8×8-inch pan.
Sift flour, baking powder, sugar, and salt together in a large bowl. Beat shortening in a separate bowl until creamy; stir into flour mixture, alternating with milk. Beat flour-shortening mixture until mixed, about 2 minutes. Add egg and beat until mixed, about 1 minute.
Combine lemon zest with blueberries in a bowl; fold into batter. Pour batter into prepared pan.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 50 minutes.