Banana and Nut Sandwich

The banana-walnut mixture can be prepared up to 2 hours ahead. Toss with 1 teaspoon lemon juice to prevent browning, then stir in mayonnaise just before assembling. Keep refrigerated in an airtight container. Butter the bread and assemble sandwiches immediately before serving.

These sandwiches are best eaten immediately. If necessary, assembled sandwiches can be wrapped tightly in plastic wrap and refrigerated for up to 2 hours, though the bread will soften. The filling alone keeps for up to 4 hours refrigerated, but bananas will continue to brown despite the mayonnaise.