Preheat the oven to 180°C. Line two 12-hole muffin trays with paper cases. Set aside.
Sift flour and cocoa into a large bowl. Stir in stevia.
Whisk buttermilk and egg and spread in a medium bowl until combined.
Add to flour mixture and stir until combined (do not overmix).
Spoon mixture into muffin trays and bake for 20 minutes or until a skewer inserted in the center comes out clean. Allow cooling completely.
Place the sugar, 1/2 cup water, egg whites, 1/2 tsp salt, and vanilla in a medium bowl.
Beat using electric beaters for 1 minute.
Place the bowl over a saucepan of boiling water and continue to beat for 5-7 minutes or until the mixture thickens and forms soft peaks.
Remove the frosting from the heat and continue to beat for 5 minutes or until the mixture is stiff enough to spread.
Frost the cooled cupcakes with this frosting.
Whisk the icing sugar mixture with orange food coloring until combined. Using the orange icing, make a web pattern.
Top with a plastic spider just for fun. Serve.