Combine the goat milk and glycerin. In a medium mixing bowl, combine the glycerin and powdered goat milk until smooth. Add fragrance oil, if using. Set aside while you prepare the base
Melt the soap base. Using a sharp knife, chop up the melt and pour base. This is just to make the melting process faster, so there's no need to be precise. Place in a large pot and melt over low heat, stirring occasionally (You can also ace the soap pieces into a microwave-safe container such as a large Pyrex measuring cup. Microwave in 30-second intervals until it is completely melted. (The soap will be very hot.)
Combine the goat milk and soap. Pour the goat milk solution into the hot, melted soap base. There may be a slightly unpleasant smell, but it will disperse as the soap cures. Mix well with a spatula until combined. If there are any stray lumps, remove them or squish them with your fingers.
Pour into molds. Pour into a bar mold. The batter will smooth out on its own. There is no need to cover or cool the soap as it hardens.
Allow to harden at least 4 hours. Let the soap cool for 4-8 hours, then remove from the molds.