Preheat oven to 350°C (175°F). Line an 8×8-inch baking pan with parchment paper.
In a bowl, whisk together almond flour, cocoa powder, baking powder, and salt.
In a separate bowl, beat eggs, melted butter, sweetener, and vanilla.
Combine wet and dry ingredients, then stir in melted dark chocolate.
Pour batter into the prepared pan and smooth the top.
Bake for 20–25 minutes, until the edges are set but the center is still soft.
Cool completely before decorating.
Melt white chocolate and pipe or drizzle a spiderweb pattern on top.
Chill for 15 minutes before slicing.