Preheat the oven to 350°F and line an 8x8-inch baking pan with parchment paper.

In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt.

Add the oil, egg, and milk. Stir until smooth, then slowly pour in the hot water while mixing until the batter is thin but uniform.

Pour the batter into the prepared pan and bake for 25-28 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool completely in the pan.

In a small saucepan, heat the heavy cream until it just begins to simmer. Remove from heat, add the semisweet chocolate chips, and stir until the mixture is glossy and fully melted.

Spread the fudge frosting evenly over the cooled cake. Let it set for 10 minutes.

Melt the white chocolate chips in the microwave in 20-second bursts, stirring between each. Drizzle the melted white chocolate in four or five concentric circles over the fudge. Drag a toothpick from the center outward in straight lines to create the spiderweb pattern.