My 'mater sammich isn't the iconic American one of white bread, mayo, and tomatoes.
I prefer dense thin slices of German landbrot (or bauernbrot - both are a sourdough wheat/rye bread that is gently tangy with a dense sponge and chewy caramelized crust giving a great mouthfeel), with rich, full fat European butter scraped across the bread. This is topped with sun-warmed, freshly picked tomatoes, sliced thin and sprinkled with a bit of salt and ground celery seed.
It is an open-faced sammich because I don't want the bread and butter to over-power the tomatoes.
Sometimes, for variety, I toast the bread and top the tomatoes with a sprinkle of basil, but it's always open-faced with the tomatoes the jewel of the sammich.
Towards the end of 'mater season, I may have my 'mater sammich made of rice crisps, butter, and 'mater slices, or even on leaves of crunchy Romaine lettuce.
How do you eat your 'mater sammich?