I put down a sheet of pasta on a floured marble surface, dotted heaped teaspoons of filling at appropriate intervals, brushed water around in between them. Then I cut squares of pasta from another sheet, each about 2cm bigger than my cutter, and placed them over each pile of filling, gently pressing down the edges before cutting each one with the cutter. The cutter is similar to a pastry cutter, but has a lip above and inside the blade that pressed down and seals the ravioli in one operation. My oversight was not expelling the air from the middle before sealing. This caused the ravioli to float straight away when dropped in the water.