HATE to see a post go with NO responses. Don't know for sure, but thinking a soak in MILD bleach solution coldn't be awful?? After mold is gone... a LONG soak (or 2-3) in clear water.

I know "they" say NOT to use any soap/detergent on baking stone things. Have a few Pampered Chef things that SIL passed my way after she got outta the demo business. Have run thru dishwasher with no (apparent) ill effects!?!

What kind of stone is the baking stone made of? The approach to sterilization and particularly rinsing will depend on porosity.

If soapstone, use of bleach and a soak rinse should be fine, as soapstone is inert to most chemicals and is non-porous. If granite, then the question would be how tightly the grains are packed; some decorative granites can be penetrated somewhat and would require very hot rinsing. A terracotta 'stone' would be porous and not a good candidate for bleaching, although multiple rinse soaks over days may suffice.

kas