There is compelling empirical evidence suggesting that more authentic learning tasks improve second language learners' motivation and learning (Long, 1996; Van Lier, 2014). However, most research on this topic has focused on Germanic and Romance L2 languages, primarily in the context of speaking skills. Little is known about the effect of task authenticity on L2 writing, especially in languages other than English. The present study investigated how increased task authenticity, operationalized as writing to a real recipient rather than an imaginary friend, affected L2 writing in Russian--a language that exhibits a high level of morphological complexity (Gilabert & Castellví, 2019; Nuss & Martelle, 2022). We adopted a mixed-methods approach to investigate participants' writing behaviors and underlying cognitive processes. Twenty-eight intermediate and advanced L1 English speakers, learning Russian as an L2, completed both more and less authentic writing tasks involving composing letters to either real or imaginary recipients. Dependent-sample t-tests revealed a significant effect of task authenticity on subordination complexity and fluency. Specifically, participants wrote texts with fewer subordinate clauses and exhibited a slower writing pace in more authentic tasks. These findings underscore the importance of investigating writing processes alongside writing products to achieve a more nuanced understanding of L2 writing.