I've been doing this for years with Palmolive shave sticks...

I never got on with shave sticks, so I put two Palmolive sticks over a cheese grater into a vintage Old Spice mug. Tiny amounts of water as I build the depth and mash the shavings down. Let dry a day, and I have a puck of one of the best shave soaps I've ever tried, with a great scent to boot!

I used it tonight, and it can rival anything I've tried ... Perhaps the extra milling?? I don't know, but it is fantastic!