Line a 12 x 17 inch jelly roll pan (or cookie sheet) with waxed paper.
Fill a small saucepan with about one inch of water. Fit the saucepan with a small bowl that covers the top of the pan but does not touch the bottom or the water (you could also use a double boiler). Bring the water to a boil over medium heat.
Place the chocolate in the bowl and heat over the boiling water, stirring constantly once the chocolate begins to melt.
Add one teaspoon of oil and stir until chocolate reaches spreadable consistency.
Once the chocolate is melted, pour over the waxed paper and spread to the edges of the pan with a spatula. Freeze for 20 minutes until chocolate is set.
Thoroughly wash and dry your bowl and place it back over the saucepan. Bring the water in the saucepan to a boil again over medium heat.
Add white chocolate and vegetable oil. Stir constantly once the chocolate begins to melt. Carefully spread the white chocolate over the milk chocolate layer.
Decorate with candies and sprinkles. Place pan back in the freezer and freeze until white chocolate layer is hardened – approximately 20 minutes.
Remove bark from pan. Peel back the waxed paper and break bark into pieces. Store leftovers in a cool, dry place.