Buttery egg sandwich filling

Sometimes simple is best. When I have next to no ingredients in my pantry or fridge, I know I can still make a classic buttery egg sandwich filling. Just a handful of ingredients and I'm instantly reminded of childhood and funerals (not the bad part of funerals, but the part where you console yourself by devouring all the food on hand - and it helps!).

In my opinion an egg sandwich filling MUST contain as much butter as it's possible to get in there, and wholegrain mustard is not optional. Herbs on the other hand are lovely to have, if you have easy access to them, but they are not a deal breaker.