Plenty, is the answer. By adding ¼ cup (measured before grinding) of finely-ground coffee beans to a half batch of tablet has resulted in almost black tarry lumps that combined sugar, butterfat and caffeine into a mallet-to-the-back-of-the-head rush.
Next time, I might use just a smidge less coffee. At the moment, it’s like a cross between full-on Rademaker’s Haagsche Hopjes and Uncle Ump’s Umpty Candy. I suspect that the RCMP will come knocking soon.