Preheat the oven to 325°F and line a baking sheet with parchment paper.
In a mixing bowl, cream the softened butter and granulated sugar until smooth.
Add the vanilla extract and salt, then mix in the dark cocoa powder until evenly combined.
Stir in the all-purpose flour until a soft dough forms.
Roll the dough to ¼-inch thickness on a lightly floured surface and cut into rounds or desired shapes.
Place the cut cookies on the prepared baking sheet and bake for 12 to 14 minutes until firm.
Cool the cookies completely on the baking sheet.
Melt the white chocolate in a microwave-safe bowl in 20-second bursts, stirring between each until smooth.
Transfer the melted white chocolate to a piping bag or zip-top bag with a small corner cut off.
Pipe concentric circles on each cookie and drag a toothpick from the center outward to create spiderweb designs.