1. Preheat oven to 350°F (175°C) and line an 8×8-inch pan with parchment paper.

2. Melt butter and dark chocolate together in a heatproof bowl until smooth and let cool slightly.

3. Whisk in granulated sugar, brown sugar, and vanilla until combined.

4. Add eggs one at a time, whisking after each addition until mixture is glossy.

5. Sift flour, cocoa powder, and salt into the chocolate mixture and fold until just combined.

6. Pour batter into the prepared pan and bake for 25 to 30 minutes until a toothpick shows moist crumbs.

7. Cool brownies completely in the pan before removing.

8. Melt white chocolate or mix powdered sugar with cream to a smooth glaze.

9. Pipe concentric circles of white icing on top and drag a toothpick from center outward to form a spiderweb.

10. Chill briefly to set the icing, then slice into squares and serve.