Preheat your oven to 350°F (175°C) while you prepare your baking pan. Line a 9x13 inch pan with foil and spray it generously with cooking spray.

In a medium saucepan over low heat, melt the butter completely. Once melted, remove it from the heat and whisk in the cocoa powder until smooth.

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

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

Pour your brownie batter into the prepared pan and spread it evenly. Bake in your preheated oven for about 25–30 minutes.

Once baked, allow your brownies to cool completely before cutting them into squares. Fill a small ziplock bag with melted white chocolate, snip off one corner, and pipe spider web designs onto each brownie.