Prepare the dough: dissolve the yeast and sugar in the warm water.
Separately, add flour and salt and mix, then add the water and start to mix, finally also the cold butter cut into chunks and work for at least 10 minutes, so that it is incorporated well.
Let it rise in a sheltered place for at least 2 hours or until doubled.
Start assembling the sandwiches: divide the dough into 16 equal cakes: shape half (8) of these into balls and roll out the other half with a rolling pin to create thin sheets.
Take 1 sheet at a time, create 4 cuts, as if to divide the circle into 4 equal segments, but leaving the center together.
Place 1 ball in the center, then place the wedges on the ball, one at a time: it will be a sort of rosebud.
Proceed like this to create the other 7 sandwiches.
As they are ready, arrange the sandwiches on the baking sheet lined with parchment paper, brush them with melted butter, then bake for about 25 minutes at 180 ° C, in a pre-heated ventilated oven and, once cooked, brush them again with butter.
The butter sandwiches are ready, let them at least cool before serving.