Complex sentence: The first of the building society's developmentwhich was designed by Frederik Bøttger, it became a sort of pilot project for the later, larger and more prominent developments built to his design, the Kartoffelrækkerne in Østerbro and the Humleby in Vesterbro.
Split into simpler sentences: The first of the building society's developments was designed by Frederik Bøttger. It became a sort of pilot project for the later, larger and more prominent developments built to his design, the Kartoffelrækkerne in Østerbro and the Humleby in Vesterbro.