• Preheat the oven to 350 degrees and line an 8x8-inch baking pan with parchment paper, creating "handles" that hang over the sides. Then spray with non-stick spray.
• In a microwaveable-safe medium bowl, melt the butter and chopped bittersweet chocolate in 20-second intervals, stirring well after every 20 seconds until melted and smooth.
• In a large bowl, whisk together the sugar, eggs, and egg yolk for 3 minutes (this step is crucial). Whisk in the vegetable oil, vanilla extract, and melted chocolate, just until combined.
• Gently fold in the cocoa powder, flour, and salt using a rubber spatula.
• Spread the brownie mixture into the prepared pan. Use your rubber spatula to spread out the batter evenly. Bake for 20-25 minutes, just until the edges are set and the middle of the brownies doesn't jiggle. You can also use a toothpick to check the center (the toothpick should come out clean with just a few crumbs).
• Allow the brownies to completely cool (at least 1 hour) before slicing them into bars.

Decorate

• In a small bowl, melt the chopped white chocolate in 20-second intervals, stirring well after every 20 seconds until melted and smooth. Cool completely at room temperature.
• Once cooled, place the melted white chocolate in a piping bag or ziplock bag. Cut a small hole in the corner and decorate each brownie one-by-one.
• Start in the center of one brownie and pipe a circle. Make a total of three circles, starting in the center and working your way out to the edge. Use a toothpick to drag the white chocolate from the center of the spiral to to the edge of the brownie. Do this several times until your brownie looks like a spider web.
• Repeat with the rest of the brownies until they are all decorated. Keep any leftover brownies in an airtight container on the counter for up to 5 days.