Preparation
Heat the oven to 350°F. Line two tins with 18 paper liners total and set them on a single rack in the middle of the oven.
Whisk the flour, cocoa, baking soda, and salt together. In a second bowl, beat the buttermilk, oil, eggs, and sugar until glossy, then fold the dry mix in until just streak-free.
Stop folding the moment the flour disappears — overworked cocoa batter bakes domed and dry.
Fill each liner two-thirds full and bake 19 to 22 minutes, until a skewer pulled from the center comes out with a few damp crumbs. Cool completely on a rack, about 45 minutes.
Once the cupcakes are fully cool, spread two-thirds of the buttercream over the tops, then roll the edges through the ruby sanding sugar to cover the frosting completely.
In a small bowl, tint the remaining ⅓ cup of buttercream with the orange gel coloring until the streaks disappear. Transfer the frosting to a piping bag fitted with a flat tip, then pipe onto the center of each cupcake so it reads like a flame. Dust the flames with the gold sanding sugar.
Finish each cupcake with a chocolate ember shard, pressed in at an angle so it stands up.
The cupcakes keep in an airtight container in the refrigerator for up to 3 days. Bring them back to room temperature before serving.
If the flames slump
Warm buttercream loses its edge fast. Chill the filled piping bag for 8 minutes, then pipe in short bursts and lift straight up — the peak sets as it cools.
Step 5. The tinted buttercream should hold a soft ribbon — thin enough to pipe, thick enough to stand.
