Wave Function Collapse (WFC) is a powerful generative algorithm, able to create locally-similar output based on a single example input. One of the inherent limitations of the original WFC is that it often requires users to understand its inner workings, and possibly make their own ad-hoc mods, to achieve satisfactory results. Besides distracting from your creative task, this strongly reduces the algorithm's effective usefulness to a small group of technical users. We propose miWFC, a novel mixed-initiative approach to WFC aimed at overcoming these drawbacks. Its main focus is on providing intuitive control to its users, in a way that matches their usual creative workflow. Among its main features, this approach provides (i) interactive navigation through design history, including controlled backtracking, (ii) precise manual editing of the output for direct expression of design intent, and (iii) interactive manipulation of tile weights, to tweak the global appearance of the output. We evaluated a prototype implementation of our approach among game artists and other creative professionals, and concluded that its features were largely considered useful and supportive of their creative work.