After the dough's first proof, line your square baking pan with parchment paper. Set this aside while you prepare your filling and assemble the rolls.
Start by mixing together the softened butter, cinnamon and sugar until you have a smooth flavoured butter paste.
Remove the dough from the refrigerator and scrape out onto a well floured work surface.
Press this into a rectangular shape and then roll out with a rolling pin to a large rectangle, about 12" wide by 15" long.
Spread the butter mixture over the surface, leaving a small gap around the edges.
Then spread the plum jam over the top. (see note)
Roll the dough from the bottom to the top, forming a tight log.
Using flavorless dental floss or thin kitchen twine, trim the ends of the log so that you remove the uneven and unfilled dough. This will be about an inch or so off of each end.
Then use the floss to divide the remaining dough into 9 equal rolls. Place the rolls in your lined baking pan and cover with a clean kitchen towel to proof at room temperature for 2 hours (until doubled in size).