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1
For the cupcakes: Position a rack in the middle of the oven and preheat to 350 degrees F. Line 12 (1/2-cup) muffin cups with paper liners.
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2
Whisk the flour with the cocoa powder, baking soda, baking powder, and salt.
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3
Beat the butter with an electric mixer at medium speed until smooth, about 2 minutes.
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4
Increase the speed to medium-high and gradually add the sugar.
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5
Beat until light and smooth, about 5 minutes.
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6
Reduce the speed to medium-low and beat in the whole eggs and yolk 1 at a time, incorporating each fully before adding the next.
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7
Beat in the vanilla.
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8
Scrape down the sides of the bowl.
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9
Bring water just to a boil in a small saucepan and remove from the heat.
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10
With the mixer at low speed, beat the flour mixture into the butter mixture in 4 additions.
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11
Drizzle in the hot water, about 2 tablespoons at a time, and mix briefly to make a smooth batter.
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12
Divide the batter among the muffin cups filling them 2/3 full.
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13
Bake until the centers of the cupcakes spring back when pressed gently, about 20 minutes.
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14
Cool the cupcakes in the tin on a rack for 10 minutes then remove from the tin and cool completely before frosting.
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15
For the frosting: Put the chocolate in a medium heatproof bowl.
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16
In a small saucepan, bring cream to a boil.
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17
Pour cream over chocolate and shake the bowl gently so cream settles around the chocolate.
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18
Set mixture aside until the chocolate is soft, about 5 minutes.
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19
Whisk gently until smooth, taking care not to incorporate too many air bubbles.
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20
Stir in 1 of the flavorings, if desired.
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21
Dip the tops of the cooled cupcakes into the frosting.
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22
(Frosting can also be chilled and whipped, then piped or spread onto the cupcakes.)
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23
Set them upright and let stand 1 or 2 minutes, until frosting is slightly set, then decorate with fresh berries, candies, or chopped pistachios, if desired.
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24
Let cakes stand on rack until frosting is completely set.
