For the bundt cakes, preheat the oven to 350˚F (177˚C).
In a small saucepan, add coffee, unsalted butter, and both cocoa powders. Cook over medium-low heat until butter is melted, stirring to make sure the mixture is smooth. Remove from heat and cool for 10 minutes.
Meanwhile, in a large mixing bowl, whisk together sugar, baking powder, baking soda, salt and flour.
Pour the chocolate mixture into the flour mixture. Mix with a spatula until combined, scrapping down the sides and bottom of the bowl.
In a small bowl, whisk together vanilla extract, egg, and sour cream. Add to the chocolate mixture and stir to combined thoroughly.
Spray a nonstick mini bundt pan with nonstick spray. Grease the pan thoroughly with a pastry brush. Pour and divide the batter evenly into the pan. Bake for 17 – 20 minutes, or until set and toothpick comes out clean. (If using a dark baking pan, check at least 5 minutes early. Cake bakes much faster in dark baking pan.)
Remove from oven and cool the bundt pan on a cooling rack for 7 minutes. Transfer the pan to a mat. Place the cooling rack upside down onto the bundt pan. Carefully hold the rack and bundt pan together and flip the whole thing over. The bundt cakes should come out easily. If not, tap the pan lightly. Remove the pan and cool the cakes completely.
For the spider webs, line a baking sheet with parchment paper.
In a small microwave bowl, add white chocolate chips. Microwave for 10 seconds, stir. Microwave for another 10 seconds and stir again. Repeat until the white chocolate is just melted. Transfer the chocolate into a pipping bag. Cut a tiny hole at the tip. Fill with melted white chocolate.
To make the web, start by piping a cross about 2-inch long. Then, pipe 2 more diagonal lines through center. Next, connect the web by piping inverted arcs, starting from the outer. Repeat to make 12 webs. Transfer the baking sheet to the fridge and chill for about 10 minutes. Reserve the melted white chocolate. After 10 minutes, pipe a dot of melted white chocolate at the back of a spider sprinkle. Glue to the web. Repeat. Keep the webs in the fridge until ready to be used.
For the ganache, prepare a double boiler. In a medium pot, add enough water to reach one inch deep. Bring to a simmering over medium heat. Reduce heat to low. Add chocolate chips and heavy cream in a large mixing bowl. Set it over the pot. Stir to melt the chocolate until just smooth. Remove from heat and pour over the cooled bundt cake. Let the ganache set for at least 30 minutes.
Carefully remove the spider webs from the parchment paper and place on the bundt cakes. Serve.