There is something oddly alien and organic about beech mushrooms that just makes them pop in photos. As an added benefit, they also taste really good, and you can usually pick up a bunch from your local Asian grocery store. Cut of the base where they are all connected and treat them like ordinary mushrooms after that. This sandwich brings out the best of the mushrooms, because they are so prominent compared to the other ingredients. We opted for a brief sautéing with olive oil and thyme.