I recently saw a smashburger burger show on Tripple-D where the cook had taken large & heavy masonry trowels with a wooden handle and cut the point off so he had what looked like a 5"-6" trapezoid to smash with. He used clarified butter to make sure it would not stick to the burger during smashing but I really like the parchment paper idea.
This is what I have it works great ...
https://www.lehmans.com/p-3304-lodg..._BING&zmam=32933335&zmas=1&zmac=20&zmap=LGPR3