Melt butter over low/medium heat and add navy bean flour. Stir until the roux becomes just a little golden brown.
Add broth/water and simmer until it is almost as thick as you like it. The gravy will continue to thicken as it cools, so remove from heat and add salt and pepper to taste.
Notes
*Navy beans ground into a fine flour using a coffee grinder. To make them more digestible I soak huge batches and then dehydrate before grinding.