After resting for a week in June 1846 at the Château de Saché in Tours, Balzac returned to Paris and began working on a short story called "Le Parasite", which he eventually developed into the novel Le Cousin Pons. He intended from the start to pair it with another novel, collecting them under the title Les Parents pauvres ("The Poor Relations"). He based the second book on a story his sister Laure Surville had written called "La Cousine Rosalie" and published in 1844 in Le Journal des enfants. Writing intensively, he produced the entire novel, named La Cousine Bette after the main character, in two months. This was a significant accomplishment owing to his bad health, but its length made Balzac's writing speed especially remarkable. One critic calls the writing of Les Parents pauvres Balzac's "last explosion of creative energy". Another suggests that this effort was "almost the last straw which broke down Balzac's gigantic strength".
Balzac's usual mode of revision involved vast, complicated edits made to galley proofs he received from the printer. When creating La Cousine Bette, however, he submitted the work to his editor piece by piece, without viewing a single proof. The book was serialized in Le Constitutionnel from 8 October to 3 December, and Balzac rushed to keep up with the newspaper's rapid printing schedule. He produced an average of eight pages each day, but was struck by the unexpected enormity of the story as it evolved. Balzac was paid 12,836 francs for the series, which was later published with Le Cousin Pons as a twelve-volume book by Chiendowski and Pétion. The first collected edition of La Cousine Bette was organized into 132 chapters, but these divisions were removed when Balzac added it to his massive collection La Comédie humaine in 1848.