Preheat the oven to 180 Deg C.
Cut the bread slices into rounds using a cookie cutter or an inverted cup. (Around 3-4 inches in diameter, you should be able to cover the inside of the muffin)
Roll the bread slices using a rolling pin.
Grease the muffin tray generously with butter.
Press the cut bread slices against the muffin cavity, so that you are able to stick it, and form a cavity.
Brush the inside of the bread with butter.
Bake in the preheated oven for 20 mins. (Keep an eye after 15 mins)
Once done cool it on a wire rack.