Prepare our Fudge Brownie recipe, and spread the batter in a greased 9" x 13" pan, or two 8" round pans. Preheat the oven to 350°F.
1. Combine the cream cheese, sugar and flour in a small bowl, and mix until smooth. Add the egg yolk and flavoring (if using), mixing until smooth once again. Transfer the mixture to a disposable pastry bag, and cut just the very tip off the end, as shown.
2. Place a small pool of the mixture in the center of the brownie batter. Draw circles around this pool, about 1 inch apart, moving out from the center each time.
3. Once the circles are drawn, take a table knife, wet the tip, and draw it back and forth through the circles.
4. The knife will draw the cream cheese filling into arcs, as you see here. Once you've gone all the way around the circles, take up your pastry bag again.
5. Use the remaining filling to trace the path where the knife travelled, to create the spokes of the web.
6. Bake the brownies for 30 minutes, until the brownies just barely pull away from the edge of the pan. The center will rise while baking, but will sink back level once the brownies are cool. Remove them from the oven and cool before cutting.