Line a baking sheet with parchment paper and set aside.
In a medium saucepan, add the semi-sweet chocolate chips, bittersweet chocolate baking bars and the oil.
Melt the chocolate over medium low heat, whisking constantly to prevent the chocolate from burning.
Once the chocolate is completely melted, pour it into the parchment lined baking sheet and spread evenly. Set aside.
In a small sauce pan, melt the vanilla milk chips over medium low heat, whisking constantly.
Remove from heat and allow to cool slightly before transferring the melted vanilla milk chocolate to a piping bag, or filling injector, fitted with a small round tip.
To make the spider webs, create several spirals on top of the dark chocolate.
Using a knife or toothpick, start in the middle of the spiral and drag it through the spiral until you get to the edge. Wipe the knife or toothpick clean. Repeat all around the spiral until you’ve created your spider web.
Put your baking sheet of bark in the refrigerator for at least 4 hours until it is set.