What is bastille? According to Amanda of Lovin' Soap says that Bastille is a term affectionately coined by soapers for soap that is made with a high percentage of olive oil. Castille is 100% olive oil soap and bastille is soap made with 70% (or more) olive oil but contains other oils or butters.
Amanda also says that Castille on its own is not very bubbly but if you add a bit of coconut oil and buttermilk you can boost the bubbles a bit but keep the mildness of the high olive oil content. Buttermilk contains sugar which helps boost the bubbles as well.
If you would like to learning how to make Buttermilk Bastille Baby Bar, check out her guest blog post on Soap and the Finer Things in Life.