Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C).
Stir together ketchup, brown sugar, 1 tablespoon lemon juice, and mustard in a small bowl until smooth.
Place beef, bread, ⅓ cup ketchup mixture, onion, beaten egg, remaining 3 tablespoons lemon juice, and bouillon in a large bowl; mix until well combined.
Form into a loaf and place into a 9x5-inch loaf pan.
Bake in the preheated oven for 1 hour. Remove from the oven and pour off fat carefully from the pan.
Spread remaining ketchup mixture over the top of loaf. Return to the oven and continue baking until no longer pink in the center, about 10 minutes more. An instant-read thermometer inserted into the center of loaf should read at least 160 degrees F (71 degrees C).
Serve hot and enjoy!