Preheat oven to 300 degrees F.
Using a 2 2/3-inch round cutter (or juice glass) cut bread into rounds. Butter both sides with melted butter and press into mini muffin tins, being careful not to tear bread. Season with salt. Bake for 10 to 15 minutes until toast are firm to the touch and slightly golden in color. Fill with desired fillings.
Recipe courtesy of Sara Moulton