Pre-crystallize the milk chocolate. (I used the seed method - melt 80% of chocolate to 45ºC, stir in the remaining 20% until working temperature of 29-30ºC is achieved).
Fill piping bag with chocolate and pipe into cups, filling them ¾ full.
Place a cooling rack over a medium-large bowl. Place the chocolate filled cups on the rack to allow the chocolate to drain out.
Flip the cups back over and place on a baking sheet to set.
Make Filling:
Melt the white chocolate.
Once melted and smooth, stir in the cashew butter and oil with a whisk.
Allow the mixture to cool to below 35ºC, so that it doesn't melt the cups when filled.
Assemble:
Pipe the filling into prepared cups and allow to set.
Cover the tops and seal the cups by piping the remaining milk chocolate over the filling.