For the cupcakes: Preheat the oven to 325 degrees F. Line a cupcake or muffin pan with 12 regular-size cupcake liners.

Place the light cream and mint sprigs into a small saucepan and cook gently for 5 minutes. Remove from the heat and leave to cool.

Sift the flour, salt, and baking powder into a small bowl and set aside. Cream the butter and sugar in the bowl of an electric stand mixer until pale and fluffy, about 5 minutes. Scrape down the sides of the bowl and add the eggs while mixing on medium speed. Scrape down the sides of the bowl again and switch to low speed. Alternate adding the flour mixture and 1 cup of the mint-infused cream, beginning and ending with the flour. Reserve the remaining cream.

Finely chop the chocolate and mix into the batter by hand.

Fill the cupcake liners two-thirds full with batter and bake until lightly golden, about 26 minutes. Cool the cupcakes in their pan for 5 minutes before transferring to a cooling rack.

For the buttercream: Beat the butter in the bowl of an electric stand mixer until pale. Add the mint-infused cream and continue beating. Reduce the speed to low and slowly add the confectioners' sugar until a creamy, medium-stiff consistency is achieved.

To assemble: Using a large, plain pastry tip, pipe the buttercream onto the cooled mint cupcakes. Garnish with a fresh mint leaf, if desired.