When Rosamund Pike sat down to tea with Emerald Fennell to discuss “Saltburn,” the filmmaker’s follow-up to her Oscar-winning “Promising Young Woman,” she ordered coffee. Fennell asked if she was going to drink it black, to which Pike stated that she was going to add milk. Recalls Pike, “So she said, ‘Oh, thank God. I think people who have their coffee black have no love in their life.’ And I just thought, ‘Okay, first test passed.’”

Pike had already read the script her agent described as “pretty delicious,” a decadent tale of obsession and excess that finds young Oxford student Oliver (Barry Keoghan) ingratiating himself into the family of classmate Felix (Jacob Elordi). Fennell wanted to offer Pike the role of Lady Elspeth Catton, Felix’s wildly out of touch mother who loves to take in charity cases — in addition to Oliver, her friend “Poor Dear” Pamela (Carey Mulligan...