* Books A$37 mln impairment benefit vs A$2.2 bln charge in 1H20 * Australian bank recovery a qtr ahead vs global peers-Citi * Targets A$8 bln cost base by 2024, smaller head office, branches (Updates share movement) SYDNEY, May 3 (Reuters) - Westpac first-half cash earnings more than tripled from last year’s plunge, helped by money it had previously set aside to cover potential COVID-19 losses, Australia’s second-largest bank said on Monday, sending shares sharply higher. The Sydney-based lender also said it will close some branches and accelerate its focus to digital banking under a cost-cutting plan unveiled on Monday that targets a 21% reduction in its cost base.