Summary

Patty Maker with ejctor for for easy handling:-)
Don´t use ABS or PLA for printing this parts!
Food save Filament, e.g. PETG, highly recommended!
Edit/Note: This especially due to the risks of growing salmonella strains in e.g. water aborbing and not fast drying PLA...

Print the round press twice - put one into the patty maker bottom.
Glue the knob together with the center pin with cyanoacrylate glue (instant glue) on the 2nd round press.

Enjoy your next BBQ!