You can make egg mayo sandwiches the night before.
Although when making egg mayo sandwiches the night before you should wrap the egg mayo sandwiches well and store the egg mayo sandwiches in the refrigerator overnight to prevent the bread from drying out and to also maintain the freshness of the egg mayo sandwiches.
The egg mayo sandwiches made the night before are best eaten within a day to maintain their quality and avoid the egg mayo sandwiches going soggy.
When making egg mayo sandwiches the night before it's best to prepare the egg mayo filling and then store it separately in the refrigerator.
Then for the freshest egg mayo sandwich, it's best to assemble the egg mayo sandwich the next day but prepare the egg mayo sandwich ingredients the night before.
If you do need to make the egg mayo sandwich the night before you can do so but you should also wrap the egg mayo sandwich tightly in plastic wrap and or place it in an airtight container.
Store the wrapped egg may sandwich in the refrigerator overnight.
And if time allows you can take the egg mayo sandwich out of the fridge up to 30 to 60 minutes before you eat or serve them to allow the bread to become room temperature warm.
And to help prevent the bread of the egg mayo sandwich from getting soggy from the mayo, you can also spread a thin layer of butter on the bread before you add the egg mixture.
Just avoid overfilling the egg mayo sandwich with the egg mixture, as this can also result in the egg mayo sandwich becoming soggy.
And if possible you should use high quality mayonnaise and fresh eggs that will also improve the flavor and texture of the egg mayo sandwich.