1. Preheat oven to 350°F and line a 9×13-inch pan with parchment paper, leaving overhangs on two sides.

2. Create a double boiler with simmering water and melt butter and semi-sweet chocolate together, stirring until smooth. Remove from heat and cool 5 minutes.

3. In a bowl, whisk together flour, cocoa powder, salt, and baking powder.

4. Whisk sugar into melted chocolate mixture until combined. Add eggs one at a time, whisking vigorously after each. Stir in vanilla.

5. Pour chocolate mixture over dry ingredients and fold gently just until combined, about 20-30 folds.

6. Pour batter into prepared pan, spread evenly, and tap pan on counter three times to release air bubbles.

7. Bake 25-30 minutes until a toothpick comes out with moist crumbs and internal temperature reaches 195-200°F.

8. Cool in pan 15 minutes, then lift onto a wire rack using parchment. Cool completely, about 90 minutes.

9. Melt white chocolate with coconut oil using double boiler method. Transfer to piping bag or plastic bag with tiny corner cut off.

10. Pipe three concentric circles on cooled brownies, then drag toothpick from center outward in 8 lines, and from edge to center between lines to create web.

11. Let chocolate set 15 minutes before cutting into squares.