Preheat oven to 350°F. Line cupcake tins with 24 paper baking cups. Set pan aside.
Whisk together cocoa and hot water until smooth. In another bowl, whisk together flour, baking soda, baking powder, and salt.
Melt butter with sugar in a saucepan over medium-low heat, stirring to combine. Remove from heat, and pour into a mixing bowl. With an electric mixer on medium-low speed beat until mixture is cooled, 4 to 5 minutes. Add eggs, one at a time, beating until each is incorporated, scraping down the sides of the bowl as needed. Add vanilla then cocoa mixture, and beat until combined. Reduce speed to low. Add flour mixture in two batches, alternating with the sour cream, and beating until just combined after each.
Fill each cupcake cup until ¾ full, about ¼ cup of batter for each.
Bake 20 minutes, rotating tins halfway through, or until a toothpick inserted in the center comes out clean. Cool 10 minutes before removing from pan. Cool completely before frosting.
Place butter in a microwave-safe bowl, heat for 15-second intervals until completely melted.
Combine cocoa powder, cinnamon, and chili powder in a small bowl. Add mixture to the melted butter, and stir until combined.
Melt chocolate in a microwave-safe bowl, heat for 20-second intervals until completely melted, stirring between each heating.
Add butter mixture and melted chocolate into a mixer fitted with a whisk attachment. Mix on medium speed until combined, about 1 minute. Scrape down the sides of the bowl if needed.
Alternately add the powdered sugar (about ¼ cup at a time) and milk (a few teaspoons at a time), mixing over medium speed between additions. The frosting should be mixed until a spreading consistency is reached. Add a small amount of additional milk, if needed until the frosting looks shiny, yet still thick. If the frosting looks slightly granular, that’s okay. It will become smooth once piped.
Add the vanilla extract to the frosting, a mix until combined, about 1 minute. Set aside.
Spider Web and Spiders
For the spider webs, roll out the fondant on a flat surface (Silpat type mat recommended), to about ⅛-inch thick. Cut out tweenty four 2-inch round or scalloped circles, transfer to a pan lined with parchment paper, and allow drying and hardening for at least 10 minutes. Using the black food-coloring marker, create a dot in the center of the circle. Make at least 12 evenly spaced lines that go outward from the dot in the center. Connect the adjacent lines with semi-circles to create a spider web look, create at least four webs.
For the spiders, use enough fondant to make 24 small spiders (about the size of a quarter). Color the fondant with black gel coloring; use a toothpick to remove some of the gel, you do not need very much to get the gray color. Work the color into the fondant until evenly distributed. Roll a small pea-sized circle for the head, and a bean-sized shape for the body. Roll out eight small gray legs, four legs on each size. Press the legs into the sides of the body to attach. Cover the fondant with plastic wrap or in a plastic bag in between use, as the fondant can dry quickly.
For the eyes of the spider, color the fondant with orange gel coloring; use a toothpick to remove some of the gel. Work the color into the fondant until evenly distributed. Roll a small pinhead-sized circle for each eye, then press on top of the head of the spider. Transfer each spider to the web; add a small amount of water to the bottom of the spider if needed to help the spider stick.
Using a large round piping tip, pipe about 2 to 3 tablespoons of frosting on each cupcake. Carefully add the fondant spider and spider web to the top of the piped frosting.
Devil's Food Cake Recipe Adapted from Martha Stewart's Cupcakes Book
Cupcakes can be stored overnight at room temperature.