All you need for this is a sharp knife. Think of this as a reverse jellyroll. You’re starting with a rolled up roast, then are going to cut it into a 1” thick sheet. Imagine the spiral of a jelly roll, that’s what you’ll be cutting.
1. Place your roast end to end, pointing away from you.
2. Make a slit down the center of the roast, about 1” deep.
3. Slide your knife into the slit you just cut. Then turn your knife so it’s almost parallel to your work surface.
4. Begin to gently saw sideways, to create a 1” think flap of meat. At first, only cut about a 1” flap, then keep cutting deeper and deeper, to open up the meat like a book.
5. Keep cutting this flap deeper and deeper, trying to keep an even thickness.