While continuously whisking, very slowly drizzle the liquid ingredients into the dry ingredients until well combined. The outcome (as pictured below) should be similar to a dry, crumbly sand and should not be a "wet" consistency. Warning: If mixture gets too wet it will activate the fizzy part of the bath bomb too soon!
TIGHTLY pack the mixture into each side of the mold then press the two sides together. Ideally let it stay in the mold overnight, then lightly tap around the mold with a spoon to very carefully open and remove bath bomb. Finished product will still be somewhat fragile, so be careful!
A Note about Molds and Gifting: I've read the stainless steel molds work best, so that's what we used with no problems. Bath Bombs (both homemade and store bought) can be fragile though, so we plan to transfer into same-size plastic molds for gifting. Alternatively, you can use a hair dryer on shrink wrap baggies made for the purpose of packaging bath bombs. I ordered a set that includes both options for our gifts this year. Either way, I would definitely make sure the DIY bath bombs are protected before handing them over!
The number of bath bombs this recipe will make is approximate. It will depend on the size of your molds.