Combine the prepared plums with the honey in a large bowl and let them marinate as you get the batter going.
In a medium bowl, whisk together the milk, sugar, eggs, vanilla, and salt. Place the flours in a separate bowl. Slowly whisk the egg/milk mixture into the flours until you have a smooth batter; it will resemble a thin pancake batter.
Grease a 7-8 cup (roughly 8 x 12 inch) baking dish or 9 inch pie plate with butter.The deeper and smaller the dish, the creamier the clafoutis. Scatter the honey-coated plums over the bottom of the dish. Carefully pour the batter over the fruit. Bake for 45 minutes to an hour or until the top is golden and crisped.