Then I read this very interesting interview with Chaon, which suggested a writing method I've used in the past and think I will try again. Chaon mentioned writing the book as a series of chapters, and trying to complete one every night. In the completed book, many of the chapters are quite short, and the narrative is somewhat fragmentary, jumping from one point of view to another, and from one time period to another.
This was more or less how I wrote my first novel, although I didn't have that much intention about it. I simply wrote short pieces I was interested in, with the hope or faith that because I was interested in them, eventually they would all fit together. Writing the connective tissue (i.e., the plot) can come later, but it may not be completely necessary in all cases. Sometimes the theme is strong enough to connect otherwise disparate sections.
In the past I've made the case for working from a pre-existing plot and allowing it to evolve as you go. Now I'm arguing that the opposite can also be effective. Just writing scenes or chapters that seem somehow related to you--or don't seem related as yet, but still intrigue you--can help you build up a deeply resonant narrative over time.
This can also work well with the 20-minute plan, which helps prevent excessive rumination and lends itself to the compact but still potentially fertile fragment.