Preheat your oven to 350°F (175°C). Line a 9x13 inch pan with foil, ensuring overhang on the edges for easy removal later, and spray it with cooking spray to prevent sticking.

In a medium saucepan over low heat, melt the butter completely. Once melted, remove from heat and stir in the cocoa powder until fully incorporated, creating a smooth mixture.

In a large mixing bowl, beat together the eggs, sugar, and vegetable oil until light and foamy. Add in the melted butter and cocoa mixture along with vanilla extract, stirring until everything is well combined and smooth.

In another bowl, whisk together all-purpose flour, baking powder, and salt until evenly mixed. Gradually add this dry mix into your wet ingredients bowl, stirring gently until just combined.

Pour the brownie batter into your prepared pan, smoothing it out evenly. Bake in your preheated oven for 25-30 minutes; check doneness by inserting a toothpick into the center.

Once cooled completely, prepare your decorative spiderwebs by melting white chocolate chips. Transfer melted chocolate into a small ziplock bag, snip one corner off, and pipe onto the brownies in spider web shapes.