Make the cupcakes: Preheat the oven to 350 degrees F. Line two 24-cup mini muffin pans with paper liners. Melt the chocolate and butter in a heatproof bowl set over a saucepan of simmering water (do not let the bowl touch the water). Whisk until smooth, then remove the bowl; keep the water simmering in the saucepan. In another bowl, whisk the sugar, flour and salt; mix into the melted chocolate. Add the eggs, one at a time, then whisk in the vanilla until smooth.
Divide the batter among the prepared cups, filling each three-quarters of the way. Bake until the cakes spring back when touched, 15 to 18 minutes. Remove from the pans and cool on a rack.
Meanwhile, make the icing: Whisk the sugar, egg whites, lemon juice and salt by hand in the bowl of a stand mixer. Empty the tea bags and add the loose tea to the bowl, then set the bowl over the saucepan of simmering water and whisk until the mixture is hot and the sugar dissolves, about 2 minutes. Transfer the bowl to the stand mixer and beat with the whisk attachment on medium-high speed until the mixture holds stiff peaks, about 5 minutes. Transfer to a large resealable plastic bag, snip the corner and pipe the icing onto the cupcakes.