1. Preheat oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper, leaving an overhang on the sides.

2. In a large bowl, whisk together melted butter and granulated sugar until well combined.

3. Beat in the eggs one at a time, then stir in the vanilla extract.

4. In a separate medium bowl, whisk together flour, cocoa powder, baking powder, and salt.

5. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.

6. Pour the batter into the prepared baking pan and spread evenly.

7. Bake for 25–30 minutes, or until a toothpick inserted into the center comes out with moist crumbs.

8. Let cool completely in the pan on a wire rack.

9. Once cooled, melt the white chocolate chips with the vegetable oil in a microwave-safe bowl in 30-second intervals, stirring until smooth.

10. Transfer the melted white chocolate to a small piping bag or a zip-top bag with a tiny corner snipped off.

11. Pipe concentric circles of white chocolate on top of the cooled brownies.

12. Using a toothpick, drag lines from the center outward through the circles to create a spiderweb effect.

13. Refrigerate for 15–20 minutes to set the white chocolate, then cut into squares and serve.