It is generally not recommended to warm up French toast in a toaster. French toast is made by soaking slices of bread in a mixture of beaten eggs and milk, then frying them in butter or oil. The cooking process in a pan ensures that the egg mixture is cooked through, and the toast becomes soft and custard-like on the inside while crispy on the outside.
If you try to warm up French toast in a toaster, it may not heat evenly or sufficiently, and you risk ending up with unevenly warmed or overly dried-out French toast. Additionally, the toaster's heating elements may not be designed to handle the moisture from the egg mixture, potentially causing damage to the toaster or creating a mess.
The best way to reheat French toast is to use an oven or toaster oven. Preheat the oven to around 350°F (175°C) and place the French toast on a baking sheet. Warm it in the oven for about 5-10 minutes, depending on the thickness of the toast and your desired level of warmth.
Alternatively, you can reheat French toast on a stovetop by using a skillet or frying pan. Heat the pan over medium heat, add a little butter or oil, and place the French toast slices in the pan. Cook each side for a few minutes until they are heated through and slightly crispy.
Regardless of the method you choose, reheating French toast on a stovetop or in an oven will yield better results than attempting to use a regular toaster.