- 36 slices thin white bread, crusts removed (see note above)
- 8 ounces (2 sticks) unsalted butter, melted
- 1 (14-ounce) can hearts of palm, drained and finely chopped
- 4 ounces sharp cheddar cheese, finely grated
- 3 tablespoons mayonnaise
- 2 tablespoons finely minced onion
- 1 teaspoon dried mustard
- 1 teaspoon grated lemon zest
- 1/8 teaspoon cayenne pepper
- Salt and pepper
Adjust oven rack to upper middle and lower middle positions and preheat oven to 325°F. Brush both sides of each slice of bread with butter; set aside.
In medium bowl combine hearts of palm, cheddar, mayonnaise, onion, mustard, zest, and cayenne. Season to taste with salt and pepper.
Spread about 1 tablespoon cheese mixture on 24 slices of bread. Arrange 1 slice of cheese mixture-coated bread on a second slice of cheese mixture-coated bread, then top that slice with one of the remaining buttered slices. Gently press the triple-decker sandwiches down to adhere, and cut each into 3 pieces.
Arrange sandwiches on two baking sheets, leaving about 1 inch between them. Bake until golden, about 20 minutes, carefully flipping the sandwiches with a spatula halfway through baking. Transfer trays to cooling racks and cool about 5 minutes before serving.