Preheat the oven to 350 degrees and line an 8-inch square pan with parchment paper.
Melt the butter in a saucepan over low heat, then remove from heat and stir in the sugar until combined.
Add the eggs one at a time, mixing well after each addition.
Stir in the cocoa powder, flour, black sesame paste, and salt until the batter is smooth and uniform.
Pour the batter into the prepared pan and smooth the top.
Bake for 25 minutes until a toothpick comes out with a few moist crumbs.
Let the brownies cool completely in the pan.
Melt the white chocolate chips in a microwave in 20-second bursts, stirring between each until smooth.
Spoon the melted white chocolate into a small zip-top bag, snip a tiny corner, and pipe a spiderweb pattern over the cooled brownies.