How to Make It
Preheat the oven to 350° and line 24 muffin cups with paper liners. Spray the paper liners with vegetable spray. In a medium bowl, whisk together the flour, cocoa powder, baking soda and salt. In a small bowl, whisk the buttermilk with the red food coloring, vinegar and vanilla. In a large bowl, using a handheld electric mixer, beat the sugar with the oil and eggs at medium speed until combined. Beat in the buttermilk mixture until blended, then beat in the dry ingredients at low speed until smooth; scrape down the side and bottom of the bowl as necessary.
Pour the batter into the prepared cups, filling them two-thirds full. Bake in the upper and lower thirds of the oven for about 30 minutes, until the cupcakes are risen and a skewer inserted in the centers comes out clean; shift the pans from top to bottom and front to back halfway through baking. Let the cupcakes cool slightly in the pans, then turn them out onto a rack and let cool completely.
Bring a large saucepan of water to a boil. Add the tapioca and boil, stirring, until softened but still slightly chewy, about 15 minutes. Drain the tapioca and cool it under running water; shake dry.
In a medium bowl, beat the butter with 1/2 cup of the confectioners' sugar until fluffy. Add the Marshmallow Fluff and beat until smooth. Fold in the drained tapioca. In a medium bowl, whisk the remaining 1 cup of confectioners' sugar with a few teaspoons of water to make a white glaze that is loose enough to pipe.
In a small saucepan, bring the cream to a boil. Remove from the heat and add the chocolate. Let stand until melted, then whisk until smooth. Transfer the chocolate frosting to a shallow bowl.
Fill a pastry bag fitted with a 1/4-inch plain tip with the tapioca filling. Poke the tip deep into the center of each cupcake and pipe in the tapioca filling; wipe off any filling that oozes out of the top. Dip the tops of the cupcakes in the chocolate frosting, then stand the cupcakes upright onto a baking sheet. Fill a pastry bag fitted with a fine tip with the white glaze. Pipe a fine spiral or concentric circles on the top of each cupcake, then drag the tip of a skewer or toothpick from the center outwards to form the spider web design. Let the frosting and glaze set before serving.